Engines cost a lot. Lycoming IO 360 is around $24000 factory rebuilt, Continental IO 550 is about $30,000 and these are not radials much less rotories and you still cant swing as big a prop as they realy need. Used of course are much cheaper but still at least half. The smaller engines like 0-200, Rotax, and the VW based engines can be flying for $4000 or less. Also the smaller planes use modern construction but look the part, kind of like the BUSA planes.