I've not tested this because I monitor my Craigslist and eBay searches in Google Reader and I check it several times per day on my smartphone (
), but you should be able to do this:
a) perform the desired search at SearchTempest.com
b) on the results page, click "Feeds For This Search"
c) download the file that they provide with a .opml extension (this is basically a list of all the Craigslist searches they did for you in a standardized format)
d) go to blogtrottr.com and sign up for an account
e) import the OPML file into blogtrottr and set up the email alerts
You can also monitor eBay searches the same way!
If you prefer the Google Reader route you can do a-c above and replace d and e inside Google Reader instead of blogtrottr (except Reader doesn't do email alerts, but it will import OPML).
One more thing, most cell phone companies allow you to send an email to a particular address to receive a text message (like email@example.com
for Verizon, where 8005551212 is replaced by your phone number). This way you could literally get a text message minutes after an ad is posted!
Please let us know how it worked out for you.