You have not told us the water pressure, or volume etc. Or if there is anything special about the valves you need
Link to SUPCON
Have you looked on eBay
I just did a quick search and found this one
http://www.ebay.com/itm/1-2-DC-12V-Electric-Solenoid-Valve-N-C-Water-Inlet-Flow-Switch-Gravity-Feed-New-/?pt=AU_Business_Industrial_Industrial_Supply_MRO&hash=itema215d9
$3.70 US sounds a reasonable price to me for such an item.
If you look on AliExpress you can get them a bit cheaper if you buy in bulk
e.g.
http://www.aliexpress.com/item/1-2-BSPP-2Way-Nylon-Plastic-Solar-Solenoid-Valve-12v-N-C-Plastic-Water-Solenoid-Valve/.html
One thing about these valves is that they are 12V and you're going to need power a power supply and power transistors to drive them.
Alternatively you could get mains voltage solenoids, which means you don't need a 12V PSU, but you'd then have mains voltages near water (never the best idea), and you'd need to drive the solenoids with solid state relays or some other device that takes the 5V output from the Arduino and converts it to be usable for mains devices
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The same power conversion is also needed if you use 12V, but the devices that will switch 12V e.g. a power FET are going to be cheaper than solid state relays.
BTW. I presume you are turning these solenoids on and off quickly to make some sort of fountain display, hence I'm not suggesting you use normal relays.
You also need to look carefully at the expected number of on / off cycles that any of these valves are supposed to do before failing, as I suspect cheap valves will not have a long MTBF or MCBF (Mean Time Between Failure or Mean Cycles Between Failure
Either way, when you multiply anything by 300 its going to end up costing you thousands of dollars to build.
There is a common irrigation-style plastic "ball" valve which has a cylinder rather than a ball. Cheap as chips but I don't know if they are rated for mains pressure, probably not I suspect.
As already mentioned, good quality ball valves need a LOT of torque to turn. I've encountered some that I could hardly operate myself, especially after a period of being static.
Zoomkat mentioned the lavatory type valve, which (if your dunnies are the same as ours) is just a float valve and these are available on all shapes and sizes. These already have a long lever so you could easily add a nut to the lever and run that up and down a threaded rod with a motor. This wouldn't need much force at all.
The problem with float valves it that they are normally used to trickle feed a tank, they may not have the flow rate you need.
@triath
Valalvax wants to control the flow rate, that can't be done with a solenoid valve (although maybe you could PWM it :))
Rob
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