a head in good shape should be about $200 bucks or so. its a good investment if you have an upgraded cam installed at the same time. Or better yet just get a head/cam combo from a shop and then send yours back as a core.
http://www.exospeed.com/engine/dseriesheadpackage.htm
Its alot of money though, so whether or not its worth it I guess would be based on what your end goal is. If its all-motor then its your only real option to add power(besides raising the compression). If your end goal is forced induction then the money would be better spent on something else like internals or the turbo kit.