Generally the difference in price is this;
-The foldable Kevlar bead is generally listed more expensive (up to about $60)
-The steel bead is sold cheaper (usually around or under $30)

I've ridden both quite a bit (the only tire I bother with anymore for riding in and around NYC, I put about 4500 miles on a set of steel beaded UGS on Manhattan streets and Central Park this summer with no issues at all, no tire has ever done that for me) and there is little difference between the two that I can feel. Weight weenies will say the Kevlar bead is lighter (it is) but fixed gear riders are rarely weight weenies... we are mostly riding steel frames after all.