By Bath I presume you mean a bathtub as opposed to a shower, though not a wholelot of difference in cost either way - tubs tend to be a bit less than showers because they go ikn quicker, but walk-in tub costs more than a regular one so probably about evens out.
Depends a lot on your job specifics, and of course the "quality" level of materials - but commonly a bathroom ceiling replaster would run about $500 plus or minus a hundred or so including painting - maybe be bit less done as part of the tub replacement.
Replacing the bath is where it gets iffy - depending on configuration and size, sometimes you can sneak a new one in without removing all the existing surround/tile if it is a bit smaller - other times, or if you want all new surround/tile then means redoing the shower walls too, as is usual for most such cases.
You might get it, in ideal conditions with very little piping modification to fit the new tub and no problems with water damage in the subfloor, for $1500-3000 range for a normal tub swapout - very rarely less. For a normal new conventional tub with new surround/tile and glass doors/splash barrier, more commonly in the $3000-5000 range I would say. However, since you are talking $2000-6000 for the walk-in tub itself (normally $3000-5000 range for normal brands) as opposed to the $300-800 for a normal tub, that cranks your cost up quite a bit, amount depending on which tub you choose.
Here is a link to one similar previous question which I found, with a couple of Answers, FYI:
https://answers.angieslist.com/How-co...
Remodeling - Kitchen and Bath would be the normal Search the List category for this type of contractor.
