http://www.tf2outpost.com/trade/11245626 Bought for 20 keys.

http://www.tf2outpost.com/trade/10532737 Selling for 21 (Yann the Human's comment suggests they were sold out at a point in time).

http://www.tf2outpost.com/trade/11199738 Easily selling for 17.

http://www.tf2outpost.com/trade/11245508 Quicksell @ 19. Offered a bud if he adds some keys.

http://www.tf2outpost.com/trade/11027422 Sold for 20 ROBO keys.

http://www.tf2outpost.com/trade/10151594 Sold a bunch for 20 keys. (mostly to the guy in link 2).

http://www.tf2outpost.com/trade/11318925 Quicksell at 18. 1 gone immediately.

http://www.tf2outpost.com/trade/10647578 Possibly sold @ 20 keys.

http://www.tf2outpost.com/trade/8389943 Observe dantelololo's offer (accepted). 3 weeks ago, that all together was probably 21.5 keys.

http://www.tf2outpost.com/trade/10715923 Sold 11 at what maybe is 20 keys (Assumed from him stating that 18 keys was a low offer).

http://www.tf2outpost.com/trade/8902588 Sold a whooping 121 and completely sold out. Price is unknown, but the point is popularity.

http://www.tf2outpost.com/trade/8271995 Rejected a white blizz buckaroos hat.

http://www.tf2outpost.com/trade/11288738 Sold many @ 20. (This is not his first spell trade)

http://www.tf2outpost.com/trade/11126163 No luck with 1 bud (~25 keys)

http://www.tf2outpost.com/trade/10722194 Rejected steaming company man (1.3-1.7) for 2. Sold one @ 20 keys.