Yes, Onan parts are pretty pricey..... if you can find them. You hear me rant about the price of the Mag 18's and KT's all the time. They're cheaper than Onan's to work on! Good news is, just like most all GT's.... if you are good with tools, you can repower them.
Under edit: I don't know much about GT's outside of CC and ..... umm..... some other less tasteful
colored ones. The FF series, especially the FF24 was a monster. I had to Google it. Says they were produced to compete with the 400 JD's. Funny thing is, they actually look pretty similar. I remember as a kid seeing them in the Sears catalog and thinking how cool they were. Funny.... I forgot all about them. Be cool to see one of them, a 400 and a 982 go head to head at a plow day!