if you get your parts from rockauto.com it's fairly cheap, I think I was into parts about $300, my turbo engine just needed the valves ground not replaced, and I'm betting my combustion temp has been up there a few times

, but the turbo heads might have harder valves...
Head work on the other hand, it was $35 to surface my head (was warped), $20 to install the cam bearings I supplied, all in all it cost me $165 out the door at the machine shop and I ground my valves at work...
If you're looking for power, port the head and intake, those are the biggest restrictions, here's a pic of a stock intake port:
I don't have a pic of how the intake ports looked when I was done, it got dark while I was grinding, then apparently got distracted... both sides could use work, but the intake is the ugliest and notoriously has the best return on these engines.