Does anybody know about how much it costs to magnaflux an engine block and heads?

 

depends on where you take it, and the type of people doing it. most people would take it to a machine shop instead of a NDT lab, machine shop would be cheaper and the people less qualified. i'd have a pressure test done if i had a problem, which it soulds like you do or you wouldn't be doing heads and block. i'd also opt for dye penetrant instead of MT testing. kit would cost you around 75 dollars.