Can get the co2 bottles which are 20oz units with an on/off valve for £40. Bottom line off a paintball gun £8. Then some form of hose (can use high pressure hose from paintball guns but tends to be a bit pricey about £7 per foot)but any high pressure hose will do.£10 for fittings and some kind of spray bar. This could be controlled by you just turning the on/off valve or if you can get hold of a boost pressure switch could be controlled from that(hav'nt found a switch yet but am on the case).So in total about £60 without the boost pressure switch. Can also get the bottles filled for £1 a time.