Hi Paris.
Is your entire budget, £100 or is that what you have set aside for a marker?
Where do you intend to use the marker?
Have you thought about Goggles, Loader, Air source, pack, other clothing, at all?
If you are buying a marker, to use at a rec site, your better off just moving straight to Sup Air.
That way, you will make savings on your paint bill straight off.
Most rec sites, will still charge you the same even if you use your own marker.
If you dont have an Air source, you will have to use their bottle and will be using more paint, because the marker is easier to shoot fast.
Think a bit, before you spend any money, or you may find yourself in a corner unable to afford to play because you are in a no man's land between having your own kit and not.