From where can I buy an old model gpu?

I have a really old system and I am going to upgrade to i7 4790 and h81 mobo with 16gb of ddr3 and I need a old model gpu for this system since I don't want to spend a lot of money on this system , but a old gpu under 15k would be good ig,

Gtx 1660 super

Gtx 1650

Rtx 2060

Rx 6600

Rx 6600xt

Rx 580

Rx 6650 xt

Rx 5600 xt

Any one from this list would be at the sweet spot ig.