The former owner of my ring paid $5100 - $5200.
DH paid roughly $1300 for my e-ring in 2002. My ring came from a Kay Jewelers outlet that sells second hand jewelry (my idea).
Since Kay Jewelers has a program where a diamond can be upgraded by the original owner (they trade up for a new ring), they have to be able to do something with the old diamond. Hence, the second hand jewelry case at the Kay Jewelers outlet that is marked at 70% off the original price. They sell diamonds from both Kay and Bailey Banks and Biddle (same parent company).
In terms of price, this outlet had a wide range of second hand diamonds. There were two smaller ones that I liked and cost less, and one slightly larger that cost more. DH wouldn't hear of buying the two smaller diamonds, and I wouldn't let him buy me the one that cost more
I have a beautiful ring (I'd guess about .85 carat) that I've received many compliments on and we didn't break the bank. The DeBeers commercials all say "a diamond is forever." Indeed they are (hardest natural substance known to man, no?). Buying a second hand diamond is a far cry from buying someone's used shoes at the thrift store.
We opened a Kay Jewelers charge card account to get an additional 10% off our purchase that day. We paid off the ring and cut up the card.
I am in the camp that believes that an e-ring should not cost more than what you can afford. The meaning of the ring is what is important, and believe me, you don't want to start a marriage off in debt over it. When you are married for a while and your finances allow, then let your DH buy you an anniversary ring.
If you don't mind wearing a second hand diamond (and it could be from a ring, a pendant or jewelry other than a ring; you could even have it placed in a brand new setting if you wanted to for not that much $) then either check out the Kay Jewelers outlet program, or check the local pawn shop (I would think you would only want to do this if you are knowledgeable about diamonds, or if the shop allowed you to have the ring appraised or had a return policy). With Kay Jewelers, I knew they were reputable, so wasn't worried.
To the OP: You and your DF will find the right e-ring. Best of luck!