Imagine that you and your child (or: niece, nephew, grandchild, etc) are thinking about what the child can buy for Mom. The young girl or boy wants to get something very special for Mommy but cannot afford what he or she thinks Mommy would like. Also, there are enough drawings and paintings stuck to the fridge with magnets and so another one would not be special enough for a birthday or Mother's Day gift.
You also would like to child to understand that "money cannot buy happiness", as the saying goes, and that sometimes "the best gifts in the world are free". People who love and care about each other do things to make the other person happy - and that does not necessarily mean spending a lot of money.