A Rotax machine (and I own one) will have very low operating costs but will probably cost a lot to buy. If you want max value I would look at a Jodel. It will be on a permit so same low operating cost with just a slightly increased fuel burn (mogas). Typical cost is £13k, with shares often available around £2.5k. Expect £600 insurance £1000 maintenance / paperwork and 21lph of Unleaded. Performance similar to a 150.
Rod1