Loads of people diss the Ion but the fact of the matter is that they are probably the best value for money marker out there, and parts are available everywhere for them. Had mine for 2 years with only minor problems.....usually caused by me
The problem you have is the amount that you want to spend and the fact that you want to use CO2?
If you stretch to £200 ish then you'd have a lot more choice and could get a PMR, shocker, Angel etc etc
use the site gun for your day out and buy a proper tourney gun