I'd say it's something you could do yourself, up to a certain point.
At stage 1, you just need to port-match. Too easy.
Stage 2, open it up a little inside and taper it down towards the valve openings.
Stage 3, open it up a LOT. Bowlwork.
Stage 4, get fancy around the valves and such...
Like any porting, any professional can do a bad job if they don't know what they're doing. Most guys just hog the openings out as much as they can (which you can't do as much with a 2G) with no thought to airflow and velocity. The turbo forgives a lot, though, which is why bowlwork makes so little difference compared to doing the same thing on a NT engine.
I paid a local VW expert (since air flows the same through ANY head, and 4cyls are pretty straight-forward) that had a flowbench. Cost me around $350 for portmatching, mild porting and bowlwork (before I knew better). For getting that last hp from someone that REALLY knows what they're doing will probably cost more than you want to pay.
At least we don't have eccentric intakes like most V8s do.
