Dear A.,
You are truly "Blessed" to have a MIL like that!! Mine never even cares to see our kids or even call!! Really Sad!
So, having said that you have to do something to make her feel loved, special, and appreciated!! To me, the same old gift or type of gift just will not do it. I love to give gifts and "do" for people. I definitely agree with Diana and Jana when it comes to gifts make it more relational. Especially since she has everything.
I like to study people and notice what they enjoy doing, what they may say they would love to do or go, favorite color, what they may like to buy, hobbies, what perfume they wear, etc. Sometimes I did this with my Grandparents if I could find something to make life/a chore easier for them. Something they were not aware of- You know sometimes the gadgets you would like to buy-even cheap ones. But you have other needs and it does not make the Budget List. But I always look at those things as great gifts for the older ones in our life that have everything. Such as the Ove Glove- they sell it at Walgreens I think. The oven mitt that will withstand up to 500 degrees.
On the cheaper side but meaningful would be to "do" something for her. A gift is easy to do but to "do" something for her as she does for you. You know a Labor of Love I think would be the best and really show your heart and appreciation. Why not, cook her favorite or a special meal at your house and decorate with candles and have her and your FIL come over. Make a Banner on your computer or by hand that says "World's Greatest or Most Loved Mother in Law" Or perhaps a simple but special "tea" that you can do for her or possibly take her to. How about clean her house, and give her a manicure (Do her errands or grocery shopping for her- I know my Grandma would love when I did that for her and if I took her to lunch on top of that she was over the top!)or just pamper her for a day. Start with making her breakfast and asking her to choose what you can do for her that would mean a lot (within reason because of cost and she sounds the type that would choose accordingly).
Hope this all helps and gave you the ideas you were looking for.
A.