Several years ago we had a smaller motorhome that did not sport a built in gen, so we bought a Coleman Powermate 1850 at Costco for about $300. Now we have a different RV with gen, but keep the Coleman for emergency use around the house. It is large for its power output, and very noisy, but the price was good. Coleman no longer makes that particular model, but they now have the Pulse 1850, which I assume is similar. MSRP is $429, but I have no doubt that price can be beat.

Camping World has the Generac 1000 Portable Generator, which appears to be a tad smaller than my Coleman, is reported to be pretty quiet, and goes for $411.

Many RVers swear by the Honda® EU2000i, which I know to be very quiet for its output. But it is in the $1000 range.

I agree with some that gasoline may not be the best fuel to use, but it is readily available, can also be used in your car (assuming that it is gas powered), and with the addition of Stabil, can be store long term. A lot depends on your location, needs, and finances...