There are a lot of reasons to use natural starters (which are yeast, after all, just naturally occuring) but economy isn't one of them. You can use a very small amount of commercial yeast if you use a slightly longer rise period, and yeast, in bulk, is not expensive.
1 Pound Fleischmann's Yeast exp: Dec. 27, 2008 Fresh! - (eBay item 110194107797 end time Nov-22-07 14:41:46 PST)
No connection, etc.