My mate (a forum member) had his PowerFC tuned twice in the space of 2 weeks at $600 a pop.
The first tune was absolute rubbish, even when they tried to fix it, the car ran okay but guzzled fuel like it was 60c/L. The second tune was much better but he didnt make the power he hoped for - $1200 later and he still doesnt have a tune he is overly happy with.
On another note, installing cams/gears is a process where a mechanic has had past experience in dealing with, he will know where they are to sit to get maximum gains because he would have done hundreds of them before and seen all the different combos so you're really only paying for their labour to fit and do small adjustments. There is no way they actually start from scratch on every cams/gears they install on an everyday setup.