Think prevention. At the very least, you should have a rubber tub mat, a handheld shower hose, a tub chair, and a nonskid floor rug.
If you can't afford a tub chair or bench, which cost $40 to $100, look for a small plastic chair with a back that will fit in your tub. But be cautious: Some plastic chairs are flimsy and hazardous. You'll want a sturdy chair, especially if your mom is on the heavier side.
If there's any money left, install grab bars or rails, which you can find at medical supply stores. Also make sure the lighting in the bathroom is good.
Don't be afraid to ask for hand-me-downs or loaners. Try your church or family members. Many people have equipment in storage they're not using anymore. Or you can suggest these items to friends and family as Christmas or birthday gifts for you or your mom.
Also check out secondhand stores and the Internet (for both new and used items). If possible, check the condition of used gear before paying, just in case something's been around for a few too many years.