Scrapyard challenge - scrounging parts for fun and profit

My initial ideas on this was to go as low-tech as I could.  It's only going to be cheaper than the store version if we get parts for cheap.  That doesn't mean cheap parts, but it means finding sources of good parts at cheap prices.

For example, my initial thought was to use a truck starter motor to run the mower.  They should be available cheaply at any wrecker, and most of the time they're just fine.  The question is really what are they rated to run at.  I know that starter motors shouldn't be used for more than ten seconds or so in a car, but that's because they're passing hundreds of amps to get the torque needed to crank the motor.  If a 24V starter motor could run at 42A or so (which would be roughly a kilowatt) for an hour then that'd be exactly what we need.

In the same line, use truck relays to run the motor.  Use direct drive - no belts or gears or anything.  Use a disc mower with flyback blades to avoid motor shocks when hitting rough stuff.  Use two small car batteries in series rather than a full truck battery.  Charge them with a standard battery charger.  Don't worry about amp or volt meters on the thing - keep the controls as simple as possible.  (I like readouts and lights, but keeping the thing cheap and simple is my objective here).

Is using a starter motor practical for this purpose?

Have fun,

Paul