Here is a recipe for a cheap garbage disposal cleaner/deodorizer
This is what you need:
Lemon
Vinegar
Ice trays
Knife
Cutting board
Slice Lemons and put them in the ice trays
pour vinegar over the lemons. Then Freeze.
Store in a ziplock bag.
Pop one of these little cubes in the garbage disposal and grind away! I use these all the time!