1.knock down shower, drywall, open access to drainage. 100-150
2.material: tub 100, shower head set 100, surround 100, plumbing supplies 100, floor 50. Total 450. If you need more drainage, add 50. May need paint the whole room afterwards.
Installation labor: 300.
Debris removal and cleaning: 50.
Now if someone tells you that you can go cheaper, you probably can do, but the quality of work is probably not good.