Analog video is the way to go.
EDIT:Second thought...with such short range, the 5.8 and 2.4Ghz systems are cheap and well within budget!
The simple long range video systems used by RC enthusiasts will suffice. The DragonLink systems are generally highly recommended...
An issue common with the transmitters is keeping them cool. Fine when in the sky and flying...but a cooling solution (fan+heatsink etc.) is recommended for ground or static use.
EDIT 2: Also, a better solution rather than increasing your Tx power is always having a better receiver gain. I guess you could easily have a flat panel Rx on a tripod next to you rather than relying on omnidirectional Rx.