You wont know how much the head will cost until its removed. DIY depends on your skills and your tool box. You would need a workshop manual. New heads are not all that expensive, so if someone gives you a high quote, you have the option going with new.
1HZ heads are pretty bullet proof. Usually they only blow gaskets when a radiator hose comes off at high speed.
There is not much to check on a 1HZ .Oil leaks, hard or lumpy starting when cold.
The fuel injection is the big dollar piece. Its a bit hard to tell with these. Most of the time they need a hot day and high speed to see if the pump loses pressure and slows the engine down.
