We visited the cultured Marble show room in San Jose
www.americancustommarble.com
Their price for a 3 sided bathroom wall, shoulder height, is around $1600 to
$2500. That is much more than I want to spend.




Cut Marble slab would be the MOST expensive route you could choose.
Cultured Marble is probably cheaper but I don't have a sense of how much.
Corian and similar also offer such products

I have seen "Shower Kits" at home centers that are made up usually of
molded
fiberglas panels with minimal seams. Tub and shower stores will have a
wider selection. Steam room kits are virtually sealed units completely
pre
plumbed and often fit in the same area as a corner shower.

Stone 12x12 or 16x16 or 18x18 tile can be set with no grout line. With
stone, you may not clean as much grout but you might use that time and
money
stripping and sealing it regularly instead.

Bigger tiles = less grout lines

If ceramic tile, use a sanitary cove molding at the bottom of the wall to
eliminate the 90 degree angle and eliminate the usual caulk line.

IMO wide grout lines are easier to clean than narrow lines (at the bottom
of
the curved tile edge)

Epoxy grouts are easier to clean and contain fewer ingredients tasty to
fungus.

With your existing installation, a good sealer (after cleaning and grout
patching) then use a spray on shower cleaner and you will need to clean
reletively infrequently.