If you want cheap flying, why not go microlighting? The motorgliders that are hired out are generally highly efficient powered aircraft with a reasonable to poor gliding/soaring performance. Examples of this would be the Grob 109 or the Katana (with the long wings). The ones operated by gliding clubs are operated to teach you to fly gliders and are generally not available for private hire. They also have a dreadful performance in everything they do (Super Falke). To get in the exotic stuff (ASH 25E), you'd have to be a London plumber or Compo Lawyer to afford it. Hence my suggestion of Microlights.