DO NOT use soil from your garden!!! There is too much of the possibility that you would be introducing molds, parasites, and other nasties that exist in the wild outdoors. You will end up wishing you had gone with a clean potting soil such as Fox Farms, Organicare or even any of the potting soils at wall mart. Just a warning from someone who has been there.
If money is an issue, Wal-Mart, and Home Depot have an excellent potting soil for about half of what you would pay at a 'Hydro' store.
Kellogs Patio plus, which I have used myself with very good results, is a wonderful alternative. And its only around 6 dollars per bag compared with 14.00 or so for Fox Farms.