Go talk to Gavin at Optimum code (Custom Code tuner based in Brisbane) - Optimumcode
I know he's tuned a few Jettas and is very reasonably priced.
There's a few other tuners around - Veizu, APR and others. Generally the larger tuners will have a two tier structure (Australian agent and local tuner). So you'll get 2 lots of margins = higher price. That's what I've found at least.
Suggest you decide first what you want to achieve/spend and then go from there.