Spending time with them is always a good option, but if you want to give them something, this is one of my favorite ideas, and for all three, would still fall well within your budget. I looked back through your posts, and see that you have 2 girls of perfect ages for this project.
Get 3 canvasses from a craft store, like Michaels. You can get whatever size you like and fits within your budget. Get a bunch of colors of acrylic paints (they're like $1 a bottle), and several different paint brushes, sponges, rollers, etc.
Let your daughters 'artistically' cover the canvasses with paints, using a mix of colors, just make sure at least most of the canvas is covered. Let it dry. Then have each girl dip their hands in white paint, and put their handprints on the painted canvas. Let that dry. If you want to seal it all off, you can buy a spray sealer at the craft store, which is usually right with all the paint supplies. Then write your daughter's names and ages on the back.
(Tip: If you mess up the handprints - my son wiggled one of his hands and it messed up the print - you can wipe off the excess white paint, then let it dry. Then you can just have your daughter paint over the messed up handprint area with the paint colors she originally used, then allow to dry, and re-do the handprint.)
My son did this for both of his grandmothers for mother's day a couple years ago, and they both LOVED it. They both have theirs hanging in their homes, and honestly, they really do look lovely.