If a tub has already been glazed and now it's chipping a bit, can it be reglazed? Or will it have to be sanded and then glazed? How much does this type of thing cost?

You can have a pro come in and do a reglaze but it is more of an epoxy paint than a true glaze which is fired. You can try with a kit from the paint store but I have never met anyone who was very happy with the result. Etching not sanding is how the prep starts. A pro may charge you around $200. You can do it yourself for about $40 and then call the pro when you don't like what you see.

Reglazing always results in peeling eventually. If your tub was in good shape you are better off removing the glaze and leave it because only liners do the trick and liners cost $3000.00 for the tub and the wall. I think it's ridiculous what they charge but glazing is something you keep on doing over and over.