I found a site that checks craiglists and emails updates
(craigslistpulse.com). I've been using it for about 2 weeks to check
for postings. At first I had it set so it would send emails every 15
minutes, but I ended up with a ton of emails. They also have 30, 60
and 120 minute updates. So far it's free. I don't know how long that
will last.