try some of the SCCA take off piles. they should have tires in your sizing all over the place and for almost nothing. they are used but not too much and can be used for several sessions. im actually trying to find a set for my stock 14's or possibly a set of miata BBS mesh 15's. my friend keven got a set of 4 tires (hoosiers r comps) for $85!!!
ill try and find the place for ya. my suggestion for SM and FWD would be running 15' wheels with 225/50-55/15's on the front and 195/45-50/15's on the front. or if money allows run the same tire size but use a 16' wheel in the rear for a stiffer rear. this set up will allow the car to rotate perfectly and will make it a monster in the slalom. it will also give you awesome grip powering thru and out of a corner.