I can't believe they quoted you such a high price. Thats too much for any person to afford. My son, and some friends, took out my mothers tub, and shower stall, which had bars, and a chair. Made a walk in with plenty of room and NO steps. This cost about 5,000 to do for materials. Would your community pitch in to do the labor? The whole project took some doing, but it was better than putting out that kind of money which our family just didn't have.
I would check to see if your local fire department, has some men, or know some people that could help you. If a house can be built with volunteers, like we see on tv. perhaps there is a way for this to happen. Try calling Homes for Humanity, and ask about volunteers, it may just work. We have groups of people in and around my area, who re-do homes. Some are roofers, others paint and do carpentry. There has to be a more affordable way for you to have the kind of shower that is safe. Wish you were near me, I would put my son to work. I wish you all the best. Don't give up. There has to be some help out there. ginnie (habbitat for Humanity) is the group I am thinking about.....