S.K.
I have taught preschool for many years and have used water/sand tables from fancy to cheap. We always called them sensory tables.
My best advice to you is is this...
Go to Walmart and buy two big plastic wash tubs. FIll one with sand and one with water and place them side by side on a child's table or on the floor or ground. You may be able to find pretty large ones at a Home Depot or Lowes.
This will give you the same effect as an expensive sensory table, and will be moveable, easy to clean and easy to store when not in use.
Those big water tables get dirty and icky after just a short time, especially in summer heat. They are a pain to clean properly. And to be honest with you, having one at home is amusing for a month or two. Then the kids get bored with it. Like you said, why break the bank?
There are many ideas out there for neat filler ideas. A few of my favorites have always been...
Potting soil with silk flowers and little shovels. The kids like to "plant" a garden.
Beans or rice with cups and spoons for pouring.
Various tube pasta with yarn for stringing.
Jello, or plain clear gelatin for less mess. If you have a smaller wash tub you can make it right in the tub- this way it's more fun to break it up!
Sand with plastic dinosaurs and palm trees.
When the sand is about ready to replace anyway- fill some cups with colored water and provide water droppers to drip the colors onto the sand.
Ice cubes and water droppers.
With water, it's always fun to provide some things to clean, sponges and a small bottle of watered down tear free shampoo to make the suds.
Set up a drying rack and have the wash their doll's clothing.
If you keep changing out the the contents- a sensory table can be entertaining for many hours!
Have fun!
-S.