I spent 12K in March 2013. It was 10k for the stone, and another 2k for the setting. I got it off a guy who runs a shop that is linked in with the online jewelery brokers. He scoured the selection of GIA stones, finally found one in Belgium and had it shipped in. Then we created the ring with this selection of settings. It was appraised for $15k.
It was probably more than I planned to spend, but the wife likes it so I guess it was worth it. I won about 3k on bama over ND, got my bonus, and had some money saved up so I paid for it in cash. I tell everyone that buys an engagement ring to only pay cash. If you can't come up with the cash, then you cant afford it. Financing a ring is dumb.