Garden Filler in Tucson?

Question:I built a garden over the weekend. Its roughly 16 square feet and about 18 inches deep. Filling it with 100% garden soil will cost a lot of cash. Someone suggested I find out what the "local" fill is to layer the bottom with first. For example, styrofoam peanuts is one example. If it helps, I think I will plant vegetables and herbs there next spring.

Answers:
You don't need the top soil to be that deep, 6-12" is plenty. Just fill in the bottom with whatever you can get, fill, leaves, sand or if you want to use the polystyrene packing peanuts, mix them in with your top soil.