It's anecdotal evidence. If you want some of that, my buy thread had at least 10 4 ref offers before someone offered for 2.66. It might be able to possibly get 5 ref, but tons of people are out there trying to sell for 4.

2 keys seems fair, a little less would be fair. So I say 1.5 keys minimum

I sold mine yesterday for 2 keys with minimal effort. Most people on outpost (or so it seems) have it at that price.