because, what you have described is getting into the range of 7 and 8 on a 10 scale of difficutly.
Do you want to save and re use the tiles? If so, be carefull about the removal process. Use a sharp wood chisel and remove each tile and then later remove the grout.
then tear down and take away all the drywall, go to the studs. Then remove all the nails in the studs that held up the rock.
Just strip every thing down to the bare walls.
The following is a nutshell description:
Check out the flooring and drip pan, make sure its working and not leaking. Add that thick membrane around the base of the shower and take it up three to four feet. Install your cementious wall boards. Do the corners and all.
At this point the entire enclosure should be enclosed with cementious board.
Now, the process of installing mastic and installing your tile.
Now, the process of grouting and wiping clean.
Now the process of siliconizing the grout.
Now the process of putting back all the fixtures.
Now, after this, call a contractor. This job will be in the neighboor hood of $1000 - 1200 in labor.