I built a free webapp that may be useful for such Craigslist arbitrage. It constantly crawls Craigslist for search terms in your price range and emails you the results (instantly or in a daily digest):
Trouble is, the app can't serve the user without having his or her email address on hand. I suppose I could rework the process so the user can give an email address after seeing how the interface works.
For those curious, the emails it sends are simple lists of links, sorted by keyword.
Then invite them with: Have these results emailed to you every day, enter your email here:
Also, I tried to sign up using the login form - that's not cool. If there is no match put up a page say, no such account, would you like to create it?