Hi Dave,
I know working with an autobody dealership, the quickest and cheapest method to fixing dents was not by welding.
Instead they drilled a 1/4 - 1/2" dia hole in the centre of the dent, and took a 90 degree bent rod (I think it was of stainless steel about 1/8" in diameter and 4" long), and inserted it sideways into the drilled hole, thus the bar was inbehind the panel, and there was the rest of the bar sticking straight out of the hole.
They just pulled at the bar, and the dent came out. Sometimes there was some paint chips, and this wouldn't be effective if you require more than the outer panel, but is very effective if you have a "clean dent" that doesn't have any body contours or bends that are effected. After that was done, they filled in the hole with bondo, and then touched it up with paint.
Thats the cheapest method I can think of!
Good luck!
You'll have to use a "slide hammer". Either drill a hole in your dent and nut in in the back to pull out the dent, or weld your slide hammer directly to the metal and yank it out, and grind your welded areas later.
As everyone would agree, use as less heat as possible. If your a novice at welding and you insist on applying heat then you should use an oxy-acetylene welder with a small tip to reduce stress. Stick and mig are to messy for this kind of application.
The larger the dent the more holes\welds you'll need to make.
vb, you have the right idea!