First serious suggestion dont hate me because I own I tried hard to find them by the way :D Here is the thinks I found :

Also 4 months old price needs a bump

Sellers :

Sold over 400 a rec each and 0.44 ea - http://www.tf2outpost.com/trade/18674932

100 for 4 keys - http://www.tf2outpost.com/trade/20881201

A rec ea - http://www.tf2outpost.com/trade/19117758

Tradebot 1 ref ea - http://www.tf2outpost.com/trade/18493036

1-100 levels collection - B/o 10 keys got offered 6 keys

Not much sellers so not much proof sry guys

Also classifieds http://backpack.tf/stats/Unique/Spellbook%20Magazine/Tradable/CraftableFor 0.33 /3.33/ 4/5 ref only 4 sellers

1 rec -sold - http://www.tf2outpost.com/trade/21150061

1rec-sold- http://www.tf2outpost.com/trade/21120074

Buyers:

For 1 ref - http://bazaar.tf/trade/901272 - no one posted yet

For 0.33 each - no one posted yet http://www.tf2outpost.com/trade/21237849

For bat outta hell - no one posted yet http://www.tf2outpost.com/trade/21055677

For 0.22 each - Bought 1 only http://www.tf2outpost.com/trade/21156381

problem is not much sellers around so lack of proof