http://www.tf2outpost.com/trade/8412021 - the only one on the market, that's not part of a set. Has an offer of 4 keys +1.55

http://www.tf2outpost.com/trade/8249043 - BUYING at 4 keys, so far unsuccessful

http://www.tf2outpost.com/trade/8021766 - my trade, got offered 4 keys + 2 ref + silver mk II knife (1,33-1,66) about 5 keys in total.

http://www.tf2outpost.com/trade/7789316 - got offered 4 keys, but sold it to someone different, most likely for more than 4 keys.

http://www.tf2outpost.com/trade/7666995- sold for 4keys + 2 ref

i honestly dont think this is enough proof, but there is only 1 thats not part of a set. So this is all i can find for now. If this is still up tmrw, i will try my best to find some more :) thanks for the consideration

NOTE: some trades are pretty old, but those were pretty much the best ones i could find