I replaced the 12V fan/light/Range Hood assembly in mine last year. It was two wires, four screws and matched up perfectly to the exhaust port in the wall. Much simpler than trying to rig up a replacement fan, IMHO.
The one I got is white in color and was under 75 bucks, delivered. I got it from an on-line RV parts place in Tulalitin, Oregon. Sorry, I don't have the name or website available now. Most all those range hood/fan arrays are a standard size. I saw them at three or four places on-line last year. Common part. Trick is like others said above, you gotta go to an RV supply for much of this stuff. I suppose you can make something else work but usually, the RV stuff is frequently standardized, plug and play replacement and relatively cheap if you shop around.
I like the computer fan idea, but does it move enough air?