I am hacking (actually I am in the pre-hacking phase) an RC car to do some basic motor control to start. I measured the start, running and stall current of the drive motor at 0.6A, 0.2A and ~5A respectively. I have looked at various shields including the Arduino shield, but I'm not sure about the ratings. The Arduino shield says 2A max per channel, but presumably this is steady state (under normal load). Assuming the controller doesn't experience the full stall current for more than a second or two, is it sufficient for my application?
You weren't specific with the shield you're looking at, but if it has the L293 that is rated at 1A continuous and 2A peak. It's never a good idea to go over the maximum ratings.
If you're looking for a low cost alternative you can use an ESC (as would be used with most RC cars). If your car has a permanent magnet motor (two wires) then you want a "brushed ESC". Interfacing with the Arduino is the same as with an RC servo.
If you go the ESC Route you might find some useful information here -
Duane B