Mitchel0407 gave you some decent advice. If it's all about the dollars, either rebuild what you have and perhaps go to a manual transmission. Next better choice would be a new GM crate engine. Small block GM engines are reasonably easy to work on and more or less stock crate engines can be had from many sources that don't cost an arm or a leg. I have had many z cars over the years with stock engines, V8 GM powered, stroked out big cam four br carbed car and a high hp, zillion dollar track car to mention a few. I sure had a blast with all of them!!! Like someone once said " if I had all the money I ever spent on Z cars, I'd spend it all on Z cars".