This bike online is affordable, has full suspension, and has no bottom bar! It also has really tough wheels. I think someone could make this a really cool bike, and with no bottom bar you could put a large engine on it with some fabrication.
http://www.lightinthebox.com/21-spe...-77868917370&gclid=CK3tvLC70dACFQGUfgod6DoBtA
http://www.lightinthebox.com/21-spe...-77868917370&gclid=CK3tvLC70dACFQGUfgod6DoBtA