Axel, answering you questions in order:
1-Maybe. Airstream put some (IMHO) cheapie vents like that on their coaches for a while.
2-Sounds like a Maxx-Air. There is another factory vent similar, with a plastic top, and plastic gears to open and close, the gears break frequently, and parts are NLA.
3- I would. $90 is 1/3 to 1/2 price, depending on fan and options.
4-If you pay attention to what you are doing, and are fairly mechanically adept, you should be able to perform this upgrade.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.