I can understand where you're coming from. It seems like you are not concerned with how much he spent on the ring so much as the fact that he didn't seem to put much effort into selecting it. You have a right to be upset, because a gift, whether it's an engagement ring or otherwise, is supposed to come from the heart. "It's the thought that counts," so if there is no apparent thought behind it, that really hurts.
My husband and I have been together since we were teenagers. After a few years, we started talking about the possibility of getting married. We were both still really young at the time and not in a big hurry, but we both agreed that's where our relationship was eventually headed. My husband wanted to surprise me with a proposal before we started making any definite wedding plans. At the time, we didn't have a lot of money and I was still an undergrad in college. I expressed to him that I didn't expect him to go into debt over an engagement ring, and while I would ideally like to have a ring of some sort to wear, it didn't have to be anything over the top since I knew we were on a tight budget. I was fine with something small and simple, and I couldn't imagine spending exorbitant amounts of money we didn't have on a ring.
When he did propose, it was really sweet and romantic, and of course I said yes, but he didn't have a ring at the time he proposed. I'll admit, I was a little disappointed that he didn't have some type of ring when he popped the question, even if it was small and simple, but I was still excited that he proposed. And he DID buy me a gift to mark the occasion so that he would have something to give me, which was a nice gesture, and the gift was related to the place he proposed at which made it special. He said it may be a few more months before he could get an actual ring and he didn't want to miss the opportunity to propose where he did just because he didn't have the ring yet. He said we could go browsing until then so he could get an idea of what I would like that was within our budget. That was fine with me, as I figured this way I would wind up with a ring we were both happy with and could afford.
However, in the mean time, the first thing most people did when they heard we were engaged, is they would literally grab my hand and hold it up to "see the ring", and then would get a confused look on their face when they didn't see one. I'd explain that we were still in the process of getting one, and they'd say, "Yeah, okay. That's nice." I even had a few people say, "Well, you're not REALLY engaged until you have the ring!" I'd be lying if I said it wasn't a little embarrassing, and also extremely annoying that other people were judging the status of our relationship on the lack of an engagement ring. But I think it was even more embarrassing for my husband, because when people saw the lack of a ring, they weren't judging me so much as they were judging him. In our society, there is a lot of stigma attached to something like an engagement ring, which seems to reflect more on the person who purchases the ring rather than the person wearing it. "Wow! Look at the size of that rock! He must really love her!" Or, "You call that an engagement ring? He must not think very much of her." "Can you believe he didn't get her a ring? How can he afford to provide in a marriage if he can't even afford to get her an expensive piece of jewelry?" It's hard to ignore that criticism sometimes.
So my husband and I shopped around. I discussed the possibility of getting a ring that had a different type of stone as the center as opposed to a diamond (sapphire, ruby, etc.) as I saw some really nice rings with different gemstones that were in settings I liked and a lot more affordable. Not that I wouldn't want a diamond, but most of the diamond rings in the jewelry stores that were more than little flecks were way out of our budget, and the way I saw it, it would be better to have a nice, vibrant gemstone than a poor quality diamond. But my husband really wanted to get a diamond ring. He kept insisting that an engagement ring had to at least cost "x" amount of money and have diamonds. I think this mentality was largely because he was afraid of being judged for getting me a ring that was something other than "the norm" on top of already being judged for having not gotten one yet. So I started looking just at diamond rings. I showed him the type of cut I liked, the type of setting, the color, etc. I found several that I liked and pointed them out, saying, "Something like this would be nice". I cut pictures out of catalogs, downloaded pictures online, but at the same time, I tried to stick only to the ones that were within our budget. I didn't want to make the mistake of saying, "This ring is perfect! I want this EXACT ring!" and then have it be something we couldn't afford.
As luck would have it, my husband's family had a business that involved purchasing a variety of items wholesale, and my husband had the opportunity to go to a wholesale marketplace with the business that was not open to the general public (you had to be an "approved" buyer) that included an entire building of fine jewelry. He was excited as he thought this would be the perfect opportunity to get a ring that we could afford for a much better value than the stuff at the retail stores. And I've always been a bargain hunter myself, so I was definitely not opposed. Since he knew the types of styles I liked, I was confident he would be able to find something. And find something he did! He was able to purchase a ring with lots of diamonds in it that was very sparkly, that was well within our budget, and would have retailed for at least double what it cost. Not to mention, it was a complete bridal set, so we now had the wedding ring as well!
It also didn't look anything similar to any of the styles I'd showed him or talked to him about. The only thing about it was that the center stone was the cut I preferred, but the setting was not my style at all, and it was the opposite color that I preferred. It looked like something a much older woman would wear, not a 20-something. I was actually a little upset that he didn't seem to listen to my preferences more carefully. I think he could sense my disappointment because he explained that while he did find some rings that were closer in style to the ones I'd pointed out that he would have been able to afford, he wanted to get the best ring that he could, and this one had the most sparkle that was within our budget and was the type of cut I liked. I came to realize that even though he didn't get me a ring that matched my preferences exactly, he went out of his way to get me the best with what he had, so he really had but a lot of effort into it. Eventually, the ring grew on me, and it looked better once the wedding band was added to it. And surprise! It had also came with a THIRD band that he gave me on our first anniversary. Once the entire set was complete, it really came together! So needless to say, I wear my ring proudly now and I don't have any plans to change it ever.
However, in your case, even though your guy didn't get you the ring you expected, the issue is more that he just walked into a store and bought the first cheap ring he could find without any thought or effort at all. If you haven't done so already, you need to talk to him about your feelings. Make sure you stress that it isn't the price of the ring that matters so much as how hurt you were over the fact that he didn't seem to put any effort into selecting it.
Let him know that it is important to you that he puts time and effort into selecting a ring since a gift is supposed to be reflective of the thought behind it. As a compromise, maybe you could suggest wearing this ring occasionally as a cocktail ring on your other hand since he did buy it for you, but looking at getting something with a little more thought to it as your every day ring.