Perry:

You want a reversable, so one of the aircraft ones is out. Robotics suppliers usually has cheap good ones for the antweight microbots:

Robot Power's Scorpion Mini is discontinued - was $30 (replacement Mini-2 under test)
- http://www.robotpower.com/ -

SozBots SOZDSCR2.3-X is discontinued - was $58 (could be snapped to yield 2x controllers at $29 each)
- http://www.robotcombat.com/marketplace_soz.html

Barello doesn't make one under $50, and neither does dimension Engineering

Duratrax has the Sprint at $30, and is available - http://www2.towerhobbies.com/cgi-bin...?&I=LXAMN7&P=7
HiTec has the EZXR-2 at $35, its also available - http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXDEM6

Then there is used ones on eBay, just make sure its usable with your radio.

I thought there was a way to hook up a servo controller board... like pull the casing, and where the board is wired to the motor, replace those leads to the servo's motor with the one to your traverse motor. Anyone done that? Got a link?

A 3-way (on-off-on) switch beside a servo should be enough... long as the voltage is right going to the traverse motor. Dead simple, cheap too.