I don't know if you can really powdercoat a block or head, or would want to, even if it was aluminum. With a block and head you're only going to get so far, maybe polishing or painting. Powdercoating an intake manifold, valve cover, maybe a timing cover, and various odds and ends will look nice. Exhaust manifolds would get some heat coating (Swain's White Lightning is ten times better than that Jet Hot stuff that is super thin).

Powdercoating will vary on who does it and how big it is. Wheels generally cost $50-100 to PC, also depends on what type of color you're getting.