Cost IS a major factor. In the Miata world, 1.6 and 1.8L engines are interchangeable without altering the drivetrain a whole lot. We can even slap certain Kia and Ford engines with minimal alterations. I'm looking for something easy, cheap but still an improvement on the current engine.
I'm still open to improving the engine I have as well... perhaps I can overbore it a little and increase compression a bit?
91 Supercharged Miata
99 E320 Wagon