Firstly, make sure you get a June 2003 or later one, this was the face lift and you'll get a much nicer centre console, a 6 speed gearbox and a few more shiny bits here and there.
You should very easily be able to get a face lift model for you budget a very good one at that.
Fuel costs are ok for what you get but it really depends what you compare it to. You'll get about 24mpg on average with mixed driving ...provided you don't boot it everywhere. On the motorway you can just about crack 30mpg on a good cruise and around town ...19-21mpg. The ST220 will vary a lot depending on how you drive it, if you open the throttle a lot then you'll use a lot more fuel, if not ...they are ok, about average for a V6 really.
Servicing ...couldn't tell you from experience as I didn't keep mine long enough to get it serviced, but at a guess I reckon £300 or so for a major service perhaps ...? ...there are plenty of people here who can tell you definitively though.
They are nice cars, superbly balanced for a fwd car and the steering is also very nice considering the fact that the wheels are also putting the power down. The interior is ok, perfectly acceptable and comfortable ...but if you are used to an Astra van then it'll be amazing I should think. The seats are good, nice comfy leather recaros that support in the right places and have adjustable lumbar. The exhaust note is fantastic, probably the best sounding 6 pot I can think of outside of the older Alfa V6s, it's intoxicating and is one of the best featureso pof the car imo.
Also, I think the saloons look better than the hatches, they just look classier and cleaner. That's personal preference though, hatches are far more common mind.
Quick, comfy, reliable, well balanced if you fancy a hoon, and absolutely fantastic looks in my opinion.
