This is my first price suggestion, I hope it's enough proof.

Current trades:

1. http://www.tf2outpost.com/trade/22303485 - "QS" 17 keys

2. http://www.tf2outpost.com/trade/22316296 - "QS" 17 keys

3. http://www.tf2outpost.com/trade/22255692 - 19 keys (3 days, 0 offers)

4. http://www.tf2outpost.com/trade/20616503 - 20 keys (premium user, 2 months trade, one offer of 1 buds + a key, probably retracted)

5. http://www.tf2outpost.com/trade/21671081 - 1.4 buds. (premium user, 4 weeks and literally 0 offers)

6. http://www.tf2outpost.com/trade/21110023 - offers (poorly bumped, one month. offers of 15 keys, 13 keys and planets robo glove)

Solds:

1. http://www.tf2outpost.com/trade/22073541 - quicksold for a bud, seller added 4 keys in sweets (proof - http://prntscr.com/4hq3ln )

2. http://www.tf2outpost.com/trade/21546180 - wanted 1 bud pure (couldn't get to seller)

3. http://www.tf2outpost.com/trade/22022872 - wanted 20 keys, sold for 16