Welcome,
If your after a mid range marker, You can easilly get a etek, etek 2, Ego05+06, shockers, G3, PM8, DM7, DM8 (I'd massivly recomed getting one of these, there going for dirt cheap atm, and your getting more then your moneys with for £300)
http://www.p8ntballer-forums.com/vb/showthread.php?t=112018
http://www.p8ntballer-forums.com/vb/showthread.php?t=112313
these things are a bargin, they shoot the same as a DM9 there planety of other stuff for that price range aswell from the buying/selling section on this forum.
Out of those 2 shootas I'd get the PMR, you save a shed load of money, as the Ion you'd have to upgrade it heavily... I know because I have one.
Other New gat options I'd suggest would be the Invert Mini (£200), Proto SLG (£300), the mini is just brill for the price.
Hope this helps, best of luck with your buying