We're offering our inexpert advice in all things automotive.
We might discuss your question on our podcast. Yes, this means that we've run out of ideas for episodes and are too lazy to do research.
Edit: Thanks for the questions everyone. We didn't have time to answer all of them on the show but I'll try to answer all of them on here. The episode probably won't be out for over a month since we've got a backlog of editing to do.
Adding power to a naturally aspirated engine will always be expensive. If you want cheap tuning you'll have to start with a turbocharged car. A GTI can gain 70+ hp with just a $500 software flash. For what it's worth though, I've had way more fun on track with a slow Miata than a 300 hp GTI because lightness is more desirable than power.