Pantry staples like white vinegar, lemons, and baking soda make for great cleaning products--dissolving dirt, soap scum, and hard water deposits. Mix 1 cup of white vinegar with 1 cup of water as a substitute for a spray cleaner. Sprinkle some baking soda on a sponge and get to work on grimy bathtub rings and stuck-on food in the sink.
Cost: a few extra bucks on pantry supplies
Savings: $50+ on commercial cleaners