You could try with the dint king if it is smaller than 4" or so. Just keep doing it over and over being sure the glue dries completely. If that doesn't work you can try to see if there is a paintless dent removal shop near you. It is a cheap alternative and works quite well. I once had 3 small dings removed in the rear door, and a small one in the front fender and a small scratch buffed out for around $120.
If it is to bad a shape for paintless dent removal it is going to cost you at least $300 for the old fashioned method. I just had my rear door done to remove several small dents. And they used Akzo Nobel, one of the biggest and best paint companies in the world. This paint is better than what even 3-M could put out IMO. If you don't have the money right now to do it right, just hold off for a little while then. The last thing you want is mismatched, peeling paint.