First of all, I assure you that you're not the first parent with the 'non-creativity' or money problem! Here are some good ideas:
• Does the shape of ice affect melting time?
• Does covering the mouth really help prevent the spread of germs?
• Which toilet tissue is most biodegradable?
• How does salt affect the boiling point of water?
• Which citrus fruit has the most Vitamin C?
• Does water go through the membrane of an egg?
• Which surface prevents skids?
• Are two ears better than one?
• Which brand cereal stays crunchy longest?
• Which type of insulation works best?
• How do different hair products affect the strength of hair?
• Does the type of soil affect its water carrying capacity?
We've done all of these projects. They are inexpensive and are true experiments.
Check out
http://www.24hourscienceprojects.com/guide.pdf for more information.