Single piece fiberglass and acrylic showers and tubs are relatively inexpensive and good quality products. They are usually too large to be installed in a remodeling situation but are often used in new construction.
It is also possible to purchase multi-piece tubs and shower stalls, using fiberglass or a combination of metal and fiberglass. These allow for installation after the original construction of the house. They are economical, and provide good tub and shower installation.