Holy Toledo! Are you saying you need to buy 250 to 280 separate valves?!?
Wow. I can see why you'd want them cheap.
Do you actually need that many separate water flows, or will only some be active at certain times? Are you going to have a pump big enough to drive all of those? All of them normally closed? (Closed unless you apply power.) How much flow per valve? (a trickle or gallons per minute?)