My 2002 Toyota Prius won't accelerate

My 2002 Prius stopped accelerating after I drove it about 70 miles today. The
check engine light had been on for 60 miles. Once it died, I pulled over but the
battery system didn't work at the lower speeds either, even though the lights in
the vehicle were still on. I turned the car off and it worked again and it
happened repeatedly for the last 20 miles. After it had been sitting for a while it
worked longer without dying. What could be wrong with it? I can trade it in but
it will be expensive so I'm trying to decide if it is more expensive to trade it or
fix it.

Thanks!