Do you mean 'air' as in any HPA bottle, or 'AIR' as in Angel AIR?
HPA bottles are expensive, but when you consider the pressure you're putting in them, the abuse they are designed to take and their lifespan, then I don't think £160/£170 for a fibre wrapped tank is a bad price at all.
Paintball is an expensive sport - tbh I'm amazed at how many young people play reguarly - there's no way I could've afforded to play when I was in my early teens.