I have a small set of body hammers and dollies that I got from Harbor Freight for probably less than $50. But I don't use those as much as I use improvised tools made from scrap lumber. Fender sheetmetal is very soft and doesn't take much force, or hardened steel to reshape it. I use mainly a couple sticks of hardwood with the ends sanded or ground to the approximate shape or contour of a fender. Support the fender on a workbench, place the end of the stick on the back of the ding, and tap the stick with any type hammer. I use a collapsible type clamping table... open the gap to span the dent area, lay the fender across the span.
I have also cut male and female forms from scrap 2x4's to use as "bucks", that match the proper cross section of the fender. I have heard of other people who use a broom handle, a pool ball, etc. It is not exactly like auto body work. Think outside the box.