I use Procar Soft discs, the Swedish distributor for Yokomo, Magic and more who makes them and sells them real cheap! But i run them mainly because i'm sponsored of'em
Probably about 4$ for 4 wheels
GS or Speedmind have the best rims Ive used yet. Both are strong and can take abuse. GS has the better spoked rims, and the speedmind is the better dish IMHO.