That sounds like RV dealer pricing to me, and that is typically ridiculously high for routine stuff. They probably figured two labor-hours and $125-$150/hr is common at RV dealer shops.
You can get the engine oil changed at most Ford dealers and some oil-change shops for half that or less, but finding somebody to do the generator may take some searching. It's not difficult, but many shops won't touch anything unfamiliar. The generator may be awkward to get at and messy to drain.
The best solution is to do yourself, but not everybody is up for that. And the first time you do it will be slow as you learn your way. After you do it a couple times, I'd guess 30 minutes to change engine oil and another 30-60 minutes for the genset, plus the time to dispose of the old oil at a local auto store (most any place that sells oil will accept it for recycle as well).