There are now some electric options, And a company named Pipistrel actually sell electric aircraft, but it's all way beyond my price range. And the range is not enough since we plan on doing a bit of touring in this thing if I ever finish it.
Most popular engine for ultralights now (as opposed to microlights, which are smaller and are what ultralights were in the 80's) is the Rotax 912. It's about 1.2 litres. 100 HP. Twin carb or fuel injected. You can also get a turbo charged version. But why make it more complicated. Bobby, most ultralights are capable of going over ten thousand feet. But the licence I converted to actually restricts ME to ten thousand 😄 highest I've ever flown was 8000, which was easy. But low and slow is more fun 😎