Tom: You should be able to pick up a stock Ion on these forums or elsewhere for around £100-110 posted, which leaves you enough for a reasonable hopper (an Egg, for example).
Tom just bit of advice on the co2 mate dont mean to put him off or anything but they do particulary hate Co2 The only way to run it would be to put an anti-siphon tube in it and maybe cap the gun at a slower rate of fire to prevent freezing A5's the way to go for Co2 with woodsball just get it upped a bit and your good to go
Good luck on the search
Sorry for chitchat