I echo that the toilet hose or (apparently this is the common slang for them) "bum guns" that you see in many Asian restrooms would be pretty cool to retrofit to a Western restroom (they really are more sanitary than the simple paper wipe, MHO). They are indeed pretty cheap. Scanning forums, though, there are two points I see that one would have to consider.

The first seems to be that hoses / sprayers can be little more prone to leaking or, even in proper operation, creating a bit of a spray mess vs a typical Western toilet installation. Most Asian restrooms designed around toilet hoses have floor drains, so the dangers of general flooding and water mess are a lot less. Western bathrooms typically lack full-room floor drains. This point I can honestly see, which is why the built in washlet might have to be the practical solution for many Western bathroom designs unfortunately.

A more "technical" issue is that these toilet hoses may not be "up to Western code" in some countries per a few forum posts. The impression I get is the code violations are more "technicalities" due to Western code not really considering this concept. Forum posts are not what I would consider an authority, but it is enough where I think it would be a good idea to check with a plumber to see if there's any code the sprayers could somehow violate.