By far I would think the cheapest would be with a PPC (Powered Paraglider)... $4000 (or less) for a wing... $8000 (or less) for the motor... and say $2000 for Harness, Reserve Chute, Helmet, Radio etc
The License would cost you about $2000 as well... And you can carry it in the back of your car and fly from just about any fairly open area in fair weather...
I could kick myself looking back in hindsight... I could have trained and purchased my own Aircraft for not too much more than this Ra-Aus futility has cost me over the last 3 years.... I have been for a Tandem Paraglide with Jean Luc at Carlo Sandblow... I would thoroughly recommend it...
http://www.paraglidingrainbow.com/