I can't answer your question concerning costs but, i will recommend buying Wayne's book. Buy the book and read through it a few times. Do the top end yourself. I did a complete rebuild on my 3.0 and would have started another the day I finished. It is very rewarding not to mention the huge boost in understand how these things work. If top end is what the car needs, remove the heads and send them out for machining, send the cams to Camgrinder for a regrind, when you are done I promise your frustration level will be reduced.

could be worse. try finding any parts or gaskets for an older Lamborghini!!! :)
since you stated you can R&R the engine yourself, you have the basic mechanical ability to do the top end componet removal. i would send out the parts as suggested, and then put em back together! think of how much you will learn, money is not everything when it comes to old cars.