Really depends on the type of bike and tubing, and what you expect. Anything with tubing below 531 or similar can be easily set cold, I used to do loads of them. The ordinary seamed tubing is ductile, and can normally be pulled close to the original.
I could put one hand on a bend half way down a raleigh fork, and pull from the fork end with the other. A bit stronger than lead pipe.
If you can send some pictures I might be able to suggest something.