Though I haven't used them in competition yet, this year we bought pneumatic solenoid valves from
www.automationdirect.com and they were by far a better price than festos from andymark. The five-port AVS-5211-24D (24 volt) is like $22 compared to festo am-0888 at $119. A-d also sent a $30 coupon in the KOP. Note that the a-d valve is significantly larger in size than the festo.