Epsom salt is dirt cheap at any drugstore, like CVS. Baking soda and table salt can, of course, be purchased from any grocery store.
I have been purchasing gypsum, calcium carbonate and calcium chloride from homebrew suppliers, but I am sure there are alternatives to those ingredients as well.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild