Any of the long established designs such as CGS Hawk, Phantom and Challenger with 503 DCDI engines are good. Now is a good time to buy. If you have a Sport Pilot license or better, try to get one that is N-numbered. It insures quality construction and makes it easier to transition to the Sport category.
I know it's not exactly cheap or even exactly an ultralight, but if I had the money I've always liked the air-cam on floats (2 engines). Every other rotax-powered tube-and-wire plane gives me pause when I think about carrying passengers.