Ok, this one doesn't sell at 3 keys, while people are willing at 2.5 keys.

Selling:

Offers:

http://www.tf2outpost.com/trade/9441792 - 4 days old, offered 2 keys

http://www.tf2outpost.com/trade/9154745 - 2 weeks old, highest offer is 2 keys + 2 ref.

2 keys:

http://www.tf2outpost.com/trade/9353051 - From the last suggestion, sold

2.25 keys:

http://www.tf2outpost.com/trade/9533392 - I bought both of them: http://i.imgur.com/CFxIG3u.png

2.5 keys:

http://www.tf2outpost.com/trade/9546933 - New, no offers

http://www.tf2outpost.com/trade/9548368 - My trade, just changed it to 2.5, since I had no success at 2.75 keys, my highest offer was 2.5 keys in items, retracted

http://www.tf2outpost.com/trade/9383914 - From the last suggestion, sold

http://www.tf2outpost.com/trade/9543706 - New, no offers

3 keys:

http://www.tf2outpost.com/trade/9535269 - Under 1 day old, no offers

http://www.tf2outpost.com/trade/9536889 - Under 1 day old, has 2 parts on it, no offers

http://www.tf2outpost.com/trade/9502465 - 1 day old, only offer is 2 keys

http://www.tf2outpost.com/trade/9352016 - 1 week old, only offer is from the seller above ^

http://www.tf2outpost.com/trade/9442077 - 4 days old, willing buyer, but retracted, he bought another one, don't know for how much

http://www.tf2outpost.com/trade/9438328 - 4 days old, not bumped in a while, no offers

http://www.tf2outpost.com/trade/9396431 - 6 days old, never bumped

Buying:

2 keys:

http://www.tf2outpost.com/trade/8762286 - Taken from other suggestion, got one offer 3 days ago

Conclusion:

Possible to get below 2.5 keys, but you have to be lucky to find a seller there.

A good amount of 2.5 key sellers, and 3 keys aren't successful.

Thanks for reading, please tell me what you think and vote, and have a nice one.