I havn't tried this, but this seems a good way to learn to fly inverted. Make a whip-control-type airplane: no engine, but with full set of controls, bellcrank, lines, handle. Make the lines about 8 feet long. Now swing the thing around and get it flying, then loop it over upside down and fly it around inverted. Do this over grass until you can actually do it. Cheap and realatively easy, I would think.

Jim