overstock.com carries rings. If I ever get married I'll just order a couple of their $40 rings (for me) and not care if I fuck them up.
What I have learned from this thread:
Couples that buy inexpensive rings are happier and stay together longer. Unless the ring was bought at a pawn shop.
Couples that buy expensive rings don't stay married long.
If you buy a $20,000 ring, you won't even make it to the wedding.
(edit)
to clarify, she would still get something nice, not a $40 ring. I would just want something cheap for myself. But I wouldn't be spending thousands on her either, I simply can't and she is understanding enough to realize that would be possible down the road, but not now.