Let's Make Robots!

gearing geared motor

Choice of geared motors

I was wondering what motors to use for my school project. its going to be a 4wd rover (skid steering) with a robotic arm and wireless camera. i have a chasis welded up and ti weighs only 800grams. Max target weight of the whole system including batteries is 4kg. 

i am willing to spend a maximum of $40 on them.

The problem is choice of motors. i found these geared motors. i found a seller who sells then in packs of 2. each one of them has a stall torque of 4kgcm and the max rpm speed is 300.