The idea that an e-ring cost should be equivalent to 2 months of the man's salary was actually a marketing ploy made by DeBeers a long time ago. They picked an arbitrary number and used it to increase their sales of diamonds. DeBeers also tried to spread the notion through their marketing that diamonds are rare gemstones when that is not the case at all.
I agree with the PPs, that you should pick out what feels right for you both as a couple. I can relate to you feeling like you don't want an expensive ring. I am personally terrified of wearing expensive jewelry as I am very good at losing things.
I'm glad that you realized I wasn't supporting that idea. The OP wanted to know how much "should" be spent on a ring and I figured I would pass that figure on. As for it actually being a marketing campaign, I'm not suprised..but it is very interesting to hear!
And just as a note, the "quality" of the diamond is only important for resale value...so, ya know, make sure its a perfect/colorless diamond so you can leave the man and sell the ring!
Don't get caught up in cost, it is almost like putting a price tag on how much you're worth. The only thing that matters is that you like your ring. I work for an engagement ring manufacturer and I get that question ALL the time. Here are a few things to take into consideration:
1. Get out of debt first before you even consider buying another ring
2. If you have to get one try and buy one from a place that offers a 12 month interest free period so that you can pay at your own pace
3. Don't buy from a commercial/chain store a lot of the time they have such high overhead and in order to make a profit they mark up their merchandise sky high
4. Keep in mind that this market is not regulated. You may find an engagement ring at one store and its $1,000 and you may find the same exact ring (hypothetically speaking) at another store for $4,000. Make sure you compare and contrast before you do anything.