Reglazing the bathtub you have currently is a good idea but only if the bathtub is in good condition and you have no other issues with the floor, plumbing etc.
Sometimes it's much better to just have the old bathtub ripped out, do a remodel of the bathroom and then replace the bathtub with a new one.
However if your bathroom is in good shape and you only want to fix the finish of the bathtub then it could be a good idea and option to have the bathtub reglazed.
The cost of reglazing a bathtub can be from $150.00 to $400.00 depending on who you have reglaze the bathtub and how bad the tub is when you have it reglazed.