To remove existing shower due to pan is leaking into the apartment below And for a 4x5 shower with tile floor and walls

That depends on the tile you pick,fixtures needed,type of pan and the cost of labor in your area.

Get at least 3 quotes and pick the one you like.

Chuck

The question is will it be done right? Learn the latest methods and materials to keep showers from leaking - ask at your local lumberyard or Home Depot. When you get quotes, have them put the specifics in writing, and be clear that they know their stuff. Don't go with the cheapest quote; go with the most informed and informative contractor.