Could you provide us with more information about tank? Depending on the size of your tank, you might be better off getting a 5 lb. CO2 tank and supplementing with Excel. If you have a smaller tank, then a smaller CO2 system might be fine, but anything larger than a 29G tank and the cost of the paintball CO2 system gets much more expensive in the long run. Here's a nice regulator and needle valve for cheap on Ebay:
[Ebay Link Removed]
I don't use a solenoid and run my CO2 24/7 without any issues. The only thing you have to do now is price out a CO2 cylinder and get it filled. I just recently bought a nice aluminum CO2 tank for $60 and filled it for $15 at my local beer and wine brewer store.