Conservative bump and matching the uncraftable version's price. Hard to find so people are paying a little extra to get one.

Buyers above 1 key

http://www.tf2outpost.com/trade/14893843 Paying 1 key + 1 scrap (1.02 keys)

http://www.tf2outpost.com/trade/14902982 Paying 1 key + 1 rec (1.05 keys)

http://www.tf2outpost.com/trade/14474965 Offering to pay 1 key + some crates

Offered/Sold for more than 1 key

http://www.tf2outpost.com/trade/14902022 http://www.tf2outpost.com/trade/14918557 Sold with 5 other Summer keys for a Bills painted Air of Debonair (value of 1.08 keys per key)

http://www.tf2outpost.com/trade/14058596 Has 2 buyers at 1 key + 1 rec and offers a TC + Genuine Anger (1.66 keys)

http://www.tf2outpost.com/trade/12949401 Had a buyer at 1 key + 1 ref (going off of what Wesley said it was 3+ days ago) (1.2 keys)

Sellers at 1 key

http://www.tf2outpost.com/trade/14817667 1 regular key

http://www.tf2outpost.com/trade/14902114 1 regular key

http://www.tf2outpost.com/trade/14880077 Swapping for an Orange Summer Crate Key (1 key)

Currently selling for around 2.80 USD on the market (2.44 UDS before Steam Tax). Regular keys are currently going for about 2.37 USD. Roughly a 40 cent difference.

http://steamcommunity.com/market/listings/440/Yellow%20Summer%202013%20Cooler%20Key

http://steamcommunity.com/market/listings/440/Mann%20Co.%20Supply%20Crate%20Key

Uncraftable suggestion

http://backpack.tf/vote/id/5252843b4dd7b8a81c8b4568