Trading Game Keys for TF2 Keys Question

Hello,

so I've been using Steamtrades.com for some time now, but I have never traded any of my game keys for TF2 keys. Lately aftre my friend has been telling me about them, I have become more interested in trading my games for TF2, since i can sell them for $2-ish on the steam market. I was wondering, are all TF2 keys the same with the same general pricing on the steam market? And if I were to trade my Bioshock Infinite and Tomb Raider game keys, what would be a good number of keys to ask for them? Thanks!