That sounds cheap to me - AFAIK a £500 remap will give you 220bhp (Stage 1), you need a new exhaust for 240bhp (Stage 2) - Milltek seem to be the preferred option, and a Milltek plus remap is around £2k (That's what I'm thinking about for the VX)
You need charge coolers etc. I think to get to 270...... (Stage 3) then you can just go silly with Stages 4 and 5 for 300hp+
This is all according to Thorney Motorsport anyway, which, IMO, are the guys in the know when it comes to Vauxhall tuning....
Thorney are good but courtenay are probably the best vauxhall tuner, i forgot about the full exhaust system, thats another 1k easily if you go for a miltek, you right its a lot of money to spend for the power gains you get