Pre-built showers/enclosures

cddc

Listen to Doozergirl, Andyhop, and Martinsurrey. The rest are all advising a bodge.

System

I once stayed in a hotel with one of the showers in the op! Took me about half an hour to figure out how the thing switched on... Even then I only managed to turn on the steam!!!
Op, sounds like you have a reasonable budget to do something nice and less problematic... Lots of bathroom places will do a bit of design for free and spec the fixtures and fitting out with you, might be worth a try (and easier to judge the quality of a fitting in a store)
Would give you something to discuss with a plumber/tiler too - most of the time these are no obligation design/quotes so you can source things elsewhere