Stripped pedal threading on a crank arm isn't a huge deal. In the worst-case scenario, you'd need to replace the crankset. A used or entry-level crankset may set you back $50 or so (plus bottom bracket, plus possibly tools).
But keep in mind that there may be other hidden surprises you may need to address. If you don't have tools and mechanical inclination, the bike could get expensive fast if you're paying someone else to work on it.