Not a challenge at all to find one for less than 4 keys.

All values are in keys

http://www.tf2outpost.com/trade/16795159 - 3, SOLD

http://www.tf2outpost.com/trade/16757112 - 3, SOLD

http://www.tf2outpost.com/trade/16792346 - 3, SOLD

http://www.tf2outpost.com/trade/16784724 - 3, 17 hours

http://www.tf2outpost.com/trade/16805412 - 3, 2 hours

http://www.tf2outpost.com/trade/16783758 - 3, 19 hours

http://www.tf2outpost.com/trade/16792715 - 3 keys + 1 ref, SOLD

http://www.tf2outpost.com/trade/16795199 - 3.4, 10 hours

http://www.tf2outpost.com/trade/16794995 - 3.4, SOLD

http://www.tf2outpost.com/trade/16790106 - 3.4, 14 hours

http://www.tf2outpost.com/trade/16806175 - 3.5, 1 hour.

http://www.tf2outpost.com/trade/16799835 - 3.5, 7 hours

http://www.tf2outpost.com/trade/16798101 - 3.5, 8 hours

http://www.tf2outpost.com/trade/16796224 - 3.5, 10 hours

http://bazaar.tf/trade/611059 - 3.5, 10 hours

http://www.tf2outpost.com/trade/16754232 - 3.5, 1 day

http://www.tf2outpost.com/trade/16797803 - 3.6, 8 hours

http://www.tf2outpost.com/trade/16762071 - 3.6, interested buyer

http://www.tf2outpost.com/trade/16762032 - 4, sold

http://www.tf2outpost.com/trade/16669548 - 4, sold

http://backpack.tf/classifieds/search/id/52b48f824dd7b8d95b8b4567 <-- 2 at 3 keys, many at 3.5 keys and above.

3 keys is still looking a bit quicksellish for now.

Please keep comments friendly and relevant (I'm talking to you big Mizore)