Replacing crank arms on Windsor 4500
So my dad rides my mtb everyonce in a while and I actually encourage it. After recently riding some trails though, I left my clipless pedals on and he put on the platform ones wrong and stripped the threads. I noticed when I was trying to take off the pedals the reverse thread for the left side wasn't moving when I would do it the right way and when I looked at the pedal, he had put the left on the right and the right pedal on the left.... I unscrewed the pedals all the while smelling burnt friction metal and when I tried to see if the clipless would go on nothing.
THE POINT IS...
I need to replace my cranks, no? Is there a way to rethread the crank arms? Is this cost efficient? So what can I get to replace them? All bikesdirect says is that they are TruVativ Aluminum Triple 22/32/42. I don't know the size and I can't measure them right now but the bike is 15" frame (I'm 5'3") so please guide me in what crank arms to get. I would want to get something of the same quality or slightly better but I'm not seriously into riding (why I only spent $350) and I was checking ebay.
ALL ADVICE WELCOME AND THANKS IN ADVANCE!