One way to get around the avgas cost and the A&P mechanic requirement for certificated planes is to own an experimental plane that uses mogas and allows owner to do most maintenance. If you build it yourself, you can obtain a Repairman's Certificate that's good for life on that plane. If you buy one second-hand, you can still do the maintenance work but need an A&P to do the annual condition inspection, still much cheaper than paying a mechanic for routine maintenance. My Pulsar with a 912 Rotax engine burns 4 gal mogas/hr at 135 mph cruise. And I do all the maintenance on it.
Bob H