Real-time web traffic alert notifications (email or SMS) on the cheap?

I'm a big fan of New Relic. One of the services they provide is alerts when your traffic goes up unexpectedly above a predetermined level.

Does anyone have a favorite, inexpensive "traffic alert" tool that can be used on a small site--a site that's not yet big enough for monthly payments of $150 for New Relic Silver (or even the $36 price tag for New Relic Silver on Heroku). Maybe a nice little does-just-one-thing-well tool that's $2-3/month or something.

The closest I've found are Clicky and Chartbeat, both of which seem to have real-time alerts for just under $10 a month. That's not bad, but it's more than $2 or $3.

A server-side tool in Ruby would be preferable to a client-side tool in JavaScript. Because a server-side tool would also track API traffic.

I know Google Analytics sends email alerts but they're daily. I'm thinking more of a "you've been slashdotted" kind of thing where you can know in a few minutes.

Thanks! And if no one knows about one maybe I'll write one myself.

Brian

for a cheap simple monitor tool for a site that is up or down -