With Mother's Day around the corner and as an octogenarian, I would like to suggest some ideas she might like rather than "stuff" to accumulate. Give her one day a month of YOU.
Get a mani/pedi together, have lunch, go to the museum or any other activity readily available. Living on a limited budget why not a grocery gift card so that she can splurge? Prepay her electric bill or rent. Most important of all make her a part of your life, invite her to participate in the things that are important to you. She may not always accept but loves the idea that you cared enough to ask.
She gave you the first 18 years of your life, surely you can spare one day a month of yours. Consider the fact that you probably don't have too many more years with her so make the most of what you do have.