Duke is right. There is no formal profession of "tuner" in relation to cars. What you do have is mechanics or shop owners who can "tune"... but there's no formal education or degree for car-tuning.
We're thinking of opening a trade course in it, though. Knowledge of automotive electronics and tuning helps auto-mechanics round off their shop skills with something that's useful enough for them to seek gainful employment with OEMs, aftermarket shops, the government (dyno and emissions testing) and etcetera.
I'm talking about tuning here in the sense that you are tuning engines... optimizing fuel and ignition maps, running dynos (and actually understanding them...), designing exhausts, learning how to deal with sensors and emissions issues when designing/fabricating aftermarket parts... etcetera...
It's an art... and at the moment, it requires lots and lots of self-study and experience. I'm studying it, myself, now, but I think I started quite too late. It's hard to juggle two day jobs and a time-consuming hobby.
What do tuners make? It depends. If they own their own shop, quite a bit. If they're working for someone else, they make what any other mechanic or master mechanic makes, usually.
I'd say: go for it. Get that formal education in Automotive Engineering, and study tuning on the side (lots and lots and lots of books on this). But be aware, the field is moving really fast. Many new OEMs are so electronically sophisticated and have such complex and interconnected electronics and emissions systems that advanced knowledge of computer programming is almost a necessity for the modern tuner.