cheap long lasting options for battery?
9V batteries are not meant for high-current discharge, as you would find when powering a motor. Not only that, they are low capacity. If you need to power motors, you should use batteries such as C or D cells in series to build the voltage required, or try Lithium-Polymer (LiPo) for a rechargeable option.

On a side note, the L293 H-Bridge is a poor choice of H-Bridge these days, especially for a battery-powered project, as there are more efficient motor driver ICs these days.