Wow, talk about a score....what a deal! The used blowers are few and far between, but they occasionally pop up on ebay or craigslist. I can get a new one from my buddy (dealer) for 1200, but then you have to ship it.....
Regarding the valve assembly, it's a fun job! I've put a few on, make sure you test the hydraulics before you put the seat pan/tire back on...you'll hear some squealing for a bit till the airs out. Also, I found that putting the dual O rings on that the manual recommends doesn't allow it to seat properly, and it was leaking, so I just put one on and it was fine. (on the outside 2 down to the hitch cylinder) Lastly, don't tighten up the flat plates too much, I did and had to buy another valve when i broke off the bolt...
Good luck and have fun with the snow....it's an awesome snow thrower!