NIB - $150-200. Used? No more than $125 and that's if it's barely been run. I paid $180 for a NIB/NOS P3 .28 pullstart engine. If you have a Factory Team Turbo, you could get a bit more maybe...
If it were mine, I wouldn't sell it. Mine is a real beast. Mine is in a heavy LST2 monster truck and it hauls it around pretty well. I'm impressed with it.