If it is the same Bath Fitters I have heard about, the price will floor you. I can’t see installing a plastic liner in a tub at a cost higher than materials and labor for a new tub.
I haven’t used them, but I know people who did. They eventually had to redo the work correctly. Covering over a problem just delays the repair and adds to the total cost. Most Baths that need surrounds have had leaks. This means that the walls are not sound. Unfortunately, redoing a Bath right, means tearing everything out and starting over. You’ll need a dumpster. Take out fixtures, walls, ceiling and floor. Repair any rot. Have the plumbing and electrical brought to code. Vent the fan, Insulate exterior walls. Install new tub. Install new green board and plaster. Use cement board on floor and around tub or shower. Tile floor and walls. Put in sink, med. cab, towel bars and misc. access. Lighting in ceiling, on walls, or combine the two. The problem is the cost…Depending on level of trim, it’s easy to spend $30,000.