is there really no replacement for displacement?...

There's no EASY replacement for displacement. If you don't get carried away with fuel injection and expensive turbochargers you can boost a slant six up to small block power levels for less than swapping in a V8. The rub is that you need to know what you're doing and how to set up everything for boost.

On the other hand, if you hunt down bargains on parts and a decent engine you can swap in a V8 pretty cheap too. It all depends on how much you know and how much work you're willing to do.