A replacement bathtub can cost as little as $100, but add the cost of a contractor, demolition, removal, disposal, paying a tile setter and a plumber and the total cost quickly grows to $2000 or more.
To see how difficult the process can be read these:
A good refinishing job on a bathtub should be very glossy, smooth to the touch, and have a uniform appearance. You will not get these results from a do-it-yourself kit.
Bathtub liners are pieces of PVC plastic or acrylic which are molded to the shape of a tub, placed over your existing tub, and then glued down to cover it up.
Many refinishers use a corrosive acid, usually hydrofluoric acid, to chemically etch a porcelain or ceramic tile surface in order to allow the new surface to stick. Acid in any form is dangerous.