First of all: I have about 65 keys in my backpack. So I will make a profit if this suggestion is accepted (if I decide to trade my keys).

Evidence

I looked through about 100-200 trades to find these links. I usually only post evidence where a seller and a buyer are agreeing on the price. No high buyout prices - they're almost meaningless for proving the high end of a price range. For the more extreme prices, I try to confirm that the keys actually moved from the seller to the buyer, but this can be hard because people often use the keys immediately to uncrate, so they just vanish without any trace.

2.5-2.66 ref

http://redd.it/12kp2o (sold for 2.5 D: )

http://redd.it/12kdcv (sold for 2.6)

http://redd.it/12k0u9 (accepted 2.66)

http://www.tf2outpost.com/trade/5953236 (sold for 2.66)

http://redd.it/12lhx6 (sold for 2.66)

http://www.tf2outpost.com/trade/3374900 (sold for 2.66)

http://www.tf2outpost.com/trade/5545076 (sold for 2.66)

http://redd.it/12l7dl (sold for 2.66 - 2.77)

2.77 ref

http://www.tf2outpost.com/trade/5952518 (sold for 2.77)

http://www.tf2outpost.com/trade/5955565 (selling for 2.77 ref - all 3 keys gone from bp in 15 minutes)

http://www.tf2outpost.com/trade/5875191 (2 buyers offering 2.77 for bulk purchase)

2.88 ref

http://www.tf2outpost.com/trade/5931760 (2.88 ref - buyer accepted price)

http://www.tf2outpost.com/trade/5940048 (2.88 ref - buyer accepted price)

http://www.tf2outpost.com/trade/5914865 (2.88 ref - sold: http://www.tf2outpost.com/item/1235402876)

http://www.tf2outpost.com/trade/5654145 (2.88 ref - possibly sold, but price may have been edited)

http://www.tf2outpost.com/trade/5864291 (2.88 - buyer offered, bulk price)

http://www.tf2outpost.com/trade/5875191 (2.88 - buyer offered, bulk price of 23 ref for 8 keys)

3 ref

http://www.tf2outpost.com/trade/5950582 (3 ref - buyer accepted price)

Here's a link to the other open price suggestion of 2.77-3 ref: http://backpack.tf/vote/id/5095d166ba2536e514000001

I think that suggestion is too high, which is why I posted this one, but there might be more evidence posted there

One other thing: The links I posted should all be from the last 24 hours, including the low priced ones.

If you ask me those sellers are having a mad comfortable time selling at 2.77 refined. Personally I think 2.77-2.88 is where it's at (I think keys should have a 1 scrap range).

@Hand slapper - normally I'd agree with you, but the price is really unstable at the moment, and I think a wider range reflects that. It could go back down any time