It really depends on what sort of p'ball you are looking to play.
If you are wanting the occasional walk-on or big game, a Tippmann A-5 or '98 is a good choice, nice and easy to maintain, robust and sturdy. Autocockers would be good althopugh they aren't to everyones taste.
If you are looking to move up into tournies, a good electro pneumatic setup will serve you better, consider a Wrath, Ion, Impulse, Angel etc.
£150 will get you a fairly good selection of quality second hand markers or some new low end starter markers.
Remember to budget for airsytmes and probably most importantly, a mask