One of the things that brought me two or minutes of quiet from my SPD son has been through tubs or bins of 'stuff' that he can put his hands through. Sometimes it is hard to come up with cheap ideas.
Here are some objects I have laying around my house that could be used. Containers for these could consist of shoe boxes, plastic bins, empty containers washed out, pans, pots, ect. Make sure that some of the containers you get have lids especially if the contents are messy.
Shaving cream or whipping cream
Homemade snot (I need to find a good recipe)
Dirt from outside
Scrapes of fabric
Vinegar and baking soda
Peanut Foam (if they won't eat it)