I didn't see any other on/off valves. So I am guessing the cheapest one is the 45 dollar one..
You have to check from time to time. Try Sinister Sports Paintball in Roseville. This store is small, but it mainly deals with paintball sport related items. That's where I got my Black CP used On and Off Valve for dirt cheap.
Bigboytoys in Elk Grove carries Half Paintball related sports and the rest are Nitro/Electric RC Cars.
You can always call Sinister Sports and ask if they got any used ON and Off Valves. I only mentioned the Paintball store in Elk Grove because I"m closer to there and I only go there to refill my Co2.
Was that the cheapest price for a new On and Off Valve?