If the water damage is getting into the next room, you may be talking lots of sheetrock work, flooring, some frame replacement and then the shower itself...... cost will vary depending on cheap fiberglass drop in or full tile etc etc....No way to comment on the cost....it may be dead on..... not enough info to comment

Buyers loved the original wood windows, beams and floors.

I attached a youtube clip I made of the first two floors, and the exterior to show you the layout and neighborhood.

What type of floors do you go with for longevity?

Full paint and flooring (including removing some wall paper and glued down laminate flooring), patched holes in walls, replaced cabinet doors that were missing, replaced a few lighting fixtures, reconfigured closets that were missing hardware, cleaned up back yard.

upgraded floors, bathrooms, cleaned it up.

Try Floor & Decor. 

A capex budget needs to include but not limited to: roof 25 year life span, floors 10 year life span, appliances and hot water heater 12 year life span, hvac 20 year life span, bath and kitchen remodel 20 year life span.

My grandmother (86) is getting too frail to go up and down the stairs on a daily basis, so she just stays on the top floor and makes my mom weight on her up and down the stairs. 

Capital) items like roofs, HVACs, flooring, siding, etc.