Do you play sup'air or woodsball(or both)? Does your local site provide HPA or just CO2? HPA is really the way to go, no matter what marker you're using so I'd recommend getting an HPA bottle then picking up any of the suggested markers above ("pmr (you'll get change), upped ion, shocker sft (maybe), invert mini") second-hand with the leftover dosh. If, however, you only have CO2, your choices are much more limited, as CO2 will generally wreck electro gats. DO get yourself a decent mask (JT, Events, Grillz, profilers, all go around the £40 mark on here). If you have the option (ie, your site provides it), I'd seriously recommend upgrading to HPA (0.8L steelies go very cheap), and nearly all your o-ring/velocity problems will disappear, amongst other benefits. That's what I'd recommend anyway.