So many variables! Depends on your choice of materials and construction method. Also depends on where you live and who you can get to do the work. I would guess between $1500 - $2500. Here is some important detail for you:
DEMOLITION: If you go back to studs, you can do it and be left with a big pile of rubble that has to be hauled to the dump. Is the shower on a slab or a cement float or wooden subfloor with a pan? That adds to everything. $50 (you do it) .... $300 (you hire it)
PLUMBING: Yo will want to update your shower plumbing. Materials = $175 plus plumber time $250to pre-plumb and install final parts. The shower drain might need work since you took out the pan = $50. The shower pan with waterproof membrane is custom = $400.
WALL PREP: You can use cement board but need to seal it against leakage. Walls = $9/sheet Durock @ 80+ sq ft + screws = $75. Fiber tape + Redgard sealant = $70+
TILING: At $3-$4 sq ft tile cost ($320) + thinset is bare minimum if you do it and can get hold of a tile saw, mixing paddle, trowels, etc. Hire a guy? Maybe $900 cheap to $1200.
Hope this helps!