Midwest is awfully proud of a lot of their parts. Anyway…
The valve in question, Nitra Valve AVP-31C1-24D 24VDC NSMP, is available of EBay but the cheapest I seen it now is $55/shipped, new open box. There’s some listings for New for about $43, but about $13 to ship. I found a new 1-off from a seller that was $40/shipped.
I would have bought this no matter what, but I believe mine is not functioning properly. I can hear it click/pwr on, but pwr off I hear another click but no purge.
This seller has a good price, but out of stock. The resupply date doesn’t seem too bad, but it’s pushed back a couple days since I checked it earlier this week.