In fairness, if someone can map a car themselves then fair play to them. I did some minor tweaks to my own MR2 when I had the turbo put on, due to the supplied map knocking at various points so it's not hugely difficult if you understand the theory. That said, I've no doubt any professional would've done a better job than me, and it took me hours of road testing to get it to where I was happy with it. If it hadn't been for the fact that I was enjoying the learning experience as much as anything, I'd have definitely been better off taking it to a tuner.
£400 is peanuts though, especially when it comes to modding.