2 month old price that needs adjustment.

http://gyazo.com/346d3a4d889d28f5345c637ecc82971c - Classifieds show 3.66 sellers and 4 ref sellers.

http://www.tf2outpost.com/trade/9396295 - Selling at 3.66

http://www.tf2outpost.com/trade/9364279 - Selling at a key or 4 ref

http://www.tf2outpost.com/trade/9375287 - Selling at 4 ref

http://www.tf2outpost.com/trade/8842180 - Sold for a key (4.11)

http://www.tf2outpost.com/trade/9400825 - Selling his cape for a Genuine one, and he'll add 0.33. This is the trade that made me raise an eyebrow since the genuines are 3.55-4 ref and the uniques are a key. The price is wrong.

CONCLUSION

The fact remains that 1 key is feasable, however the fact remains that many people will buy and sell for cheaper. Considering a key is 4.11 at the time of writing, I feel this is an adequate range.