If cost is literally no object, your best bet is probably Corian. If you stick to a standard size and one of the cheaper color mixes (ie, off-white, almond vs "Black Galaxy" or one of the stonelike varieties), a 3x4 pan will probably run about $1,200 (at least, that's what I remember from ~3 years ago when I last researched it).
Corian shower receptors are definitely exotic items that absolutely have to be ordered online, because they're strictly a niche product -- they're expensive and have zero "wow" factor for builders showing off a spec-built home because all the "affordable" ("A" cost) versions look like cheap plastic, and the nicer colors are breathtakingly expensive by any sane standard.
That said, if you can afford it... and especially if you can afford to do the walls with it, too, it's probably the most maintenance-free shower you could possibly have. From what I remember reading, the gold standard is to hang the wall panels, then bevel 1" x 1" pieces and fuse one into each corner and the wall-floor wall-ceiling borders.
Unfortunately, I think the "100% solidly-fused" shower idea only works somewhere that's completely non-seismic, like Florida. Someplace like California, even a minor earthquake would probably cause some REALLY expensive damage to it (as in, stress fractures and/or splintering) unless you settled for caulked joints (so they could jiggle a bit without tearing each other to shreds). On the other hand, I remember reading about a dotcom millionaire in Silicon Valley who wanted it really badly, so he brainstormed with his friends and had the contractor build him a reinforced concrete shower box using ICF (theory: in a bad earthquake, the whole box would move as a monolithic unit while holding the Corian motionless relative to the other Corian, with the foam additionally acting as shock-absorbers). I remember people commenting that someday, the rest of his home might be reduced to rubble by "the big one", but at least he'd still be able to take showers ;-)