This experiment looks at how the volume of a gas changes with heating and cooling. You can make a cold bath using isopropyl alcohol and dry ice (the alcohol can get very cold - much colder than water - without freezing). Then take a water bottle and run it under hot water. Put the cap on, submerge it in the bath and see what happens.
Do you have any recommended science experiments using inexpensive materials? Did you find these ones useful? Let us know what you think.