You are missing a bit more than just a pedal, the left crank arm is missing. The Bottom Bracket looks higly corroded as well.

That bike looks to be extreme low end, would guess it had been dumped as missing this part, and the orginal owner saw it was cheaper to dump than fix. Would suspect the cost of replacing the crank arm, pedal & tires as you say are rotted will be similar to buying a whole new bike; unless you can find another scrap bike with the parts you need, as you will probably have to buy a complete crank, and pair of pedals.