I don't want to. Shop around some more if you need to save. If you're actually buying keys at face value I can possibly accommodate you cheaper with $10 spent on Backpack Expanders in TF2 store.
you can probably get killing floor for like 2 keys if you search around. Alot of traders here don't like to reply to threads and wait for people to post on theirs
just do a search for killing floor, post on everyones thread, and you'll get a shit of load of responses tomorrow. Unless youre in a hurry now to play it