I'd say add extra $200 to frame and sheath the opening and $1000 to patch the stucco. I'd keep the window 5' above the floor of the tub to save eliminate the need for tempered glass.

I'd pull the window in flush with the interior wall, foam it and use a waterproof membrane to seal the window to the wall if you use the existing opening.

Glass block works well when the window is very low and takes on water, picture windows work as well, double-hungs can take on water that might freeze in the sill area .

Prices will vary. Stucco is a mixed bag and unless you are in an area where it is prevalent and there are some good contractors that work in it, it can be all over the price as well as the workmanship.

Todd's information is spot on.

Thanks so much! I live in Orange County, CA, so while there have been freezing nights, it is uncommon. stucco is common here, but at $1k, I think I'll just keep the window. It's placement is less than 5' from the floor, so I will need tempered. I actually called our city inspector and they said any window in a shower had to be, so no getting around that!