Mask was the first thing I bought
As soon as you've got your own thermal mask you will see how much better they are compared to rentals! I got one of the cheaper protos off o' Just (knowing full well that I'll sell/chuck it as soon as I have enough monies for an i4 in Red Cloth)
After that, a nice little steelie + pods (off the forums here) as well as a very nice £125 gat (need to find a new board since its from 2007...)
Hopper, jersey and pants I all got off of team members who had spares going
All in all, I've spent just about £250 on equipment and its all working out really well! Have a serious look on the For Sale section, everyone's really nice and remember that there are plenty of FS threads lying around, so go back 10/20 pages as well.
(p.s. you will soon be addicted to paintball! Make sure you have a big enough hole in your wallet)