I'm so sorry to hear about your grandmother's injury! And I commend you for wanting to help keep her safer in the bathroom. One of specializations as a kitchen and bath designer is aging-in-place. Here are some less expensive alternatives than a walk-in tub that you can consider for your grandmother:
1) If she has a tub/shower combination, convert it to a low- or no- threshhold shower. (Use a licensed general contractor for this project.)
2) Add a bench to her shower.
3) If she lives alone, replace her current showerhead with one on a slidebar that she can use while seated on her bench.
4) If she lives with your grandfather, add a second showerhead on a slidebar that will always be in the right position while she bathes seated.
Here are some additional, low-cost aging-in-place tips from my summer newsletter:
• Replace a standard toilet with a comfort-height version
• Add grab bars in the shower, tub and toilet areas
• Replace knob-style faucets with lever-handled faucets
• Replace a pre-code shower valve with a non-scald version
• Increase the bathroom’s lighting
• Check that the vent fan is working properly to help avoid mold
• Replace smooth, slick flooring with a less slippery textured tile.
I wish your family well and your grandmother a speedy recovery.
JTG, Tampa, Florida
PS: After October 12, you should be able to access my upcoming BobVila.com article on accessibility for whole house accessibility tips.