Why, in God's name, would you want the cheapest wheel cylinders? The brakes on a Fox are only good for one fast stop and you would compromise that by buying wheel cylinders of questionable quality? Do you have some sort of death wish or something?
they are all about the same, IMHO. best to get new vs rebuilt, but thats about it. i havent heard of any "performance" wheel (brake) cylinders. LOL.
that said, try and pick a decent brand (or brand that is known). i have used napa stuff before and it was fine (agree with M.S.). they are all pretty cheap (for other cars, dont see why stangs would be different).