Curious... Why do you want a stack of 4 magnets? It won't do anymore than two. Also, if you go with unmagnetized magnets, I doubt there would be anyone around who would have a magnetize with enough energy to magnetizer a stack of four together.
Ceramic magnets are cheeper than steel. So I gain 3/4 in for $30 bucks instead of $80 for steel billet. Checking with a couple people on getting them charged.