The way I would work it, I would ask each participant to supply a list of few armys or models. Example
name - Daz
Forum - Soulshade
Would like - Anything!
Would prefer - malifaux guild faction, 40K grey knights, 40K nids (kracken), Warhammer Empire (boghoffen).
Doesnt want - Any named Warhammer Empire characters, any thing from the lady justice boxed set.
I would then PM that on to somebody, along the lines of
Ok your choices are. - Anything.
They Would like - Grey Knights, Nids (Kracken), Malifaux guild faction.
Not interested in - Empire named Characters.
It would be more refined then that at the time, but you get the idea. Im also looking at a price of between £5 and £15, that covers most metal blisters. Ofcourse if your fealing flush, or if there is something you think the recipiant would love and you want to paint it, you can spend what you want. Just dont expect the same in return. Ofcourse the whole thing is done on the hush. Im the only person who should know whos doing what. The idea is its a 'surprise'. People can ofcourse post painting logs if they wish. People may figure out from this that its for them or the painter may actualy figure out who it is by the armys listed. If you do, keep it zipped please