Stage 1 is either software change or box.
You should expect 360-370bhp
With stage 2 you need ic and 3'dp. That should make around 400bhp. Adding intake mod, tip and a drop in should make around 410-420.
Stage 3 would be stage 2 + hybrid turbo + 3 inch turbo back ( if you have 3inch dp then you only miss 3 inch catback) should make up to around 500bhp without opening the engine.
Above 500 it gets more expensive as you should upgrade fuel pump and work on engine internals. If your turbo from stage 3 is big then it should make 550-600 above 2bars of boost.
Above is more or less universal for
280/
290/300.
I am skipping expenses for dsg or manual gear box clutch mods as this is more eacj car specific. You can be lucky or not