I found one on ebay for $40 shipped, But ive "Read" that people are getting them as low as $20ish, just need to know the part number so I can google it. Once I get it I can put my air compressor regulator/boost controller back on the compressor...lol
You CAN get them for $20-ish plus shipping, but the price and leadtime depends solely on your state's distributor (see MAC's site). MAC does NOT allow their distributors to sell out-of-state if there is an established distro in that state. They also have a 4-week lead time on all non-stocked valves, which is most valves. My local distro stocked 2 compatable valves both times I ordered, and had no problem with small orders.
I prefer the 35-series: smaller, cheaper, and lesst boost is wasted when venting. I used to get PN 35A-AAA-DDBA-1BA, but the "DB" in that PN is for 12v which their PDF doesn't list anymore. Call your distro on that on. Otherwise you can get the larger 36-series, which is 36A-AAA-JDBA-1BA for the most common valve. The 36 will be ~$5 more for the same options. If you have to order one, you can change the A in "DDBA"/"JDBA" to a different letter for longer wiring. I got a couple E's, which was 72" of wire.
I might buy a bunch more this year, since they seem to be selling more on fleabay. I also want to try some stuff with a 4-way valve. I have an idea that could use a 4-way valve to control a 5psi spring way past 25psi. Normally past 2x spring pressure boost is impossible to control.