theres one of those cheapo behringer ones, they cost about £15...i'm sure someone on here bought one, maybe they'll chime in soon!
or go to ebay or a second hand place, get a cheap crybaby. Or, maybe you could try and get a boss autowah or some other such thing.
Personally, i'd save up for a bit. A wah is one of those pedals that its important to get right, otherwise it'll really screw with your tone.