Custom SMS notifications of website updates

We need to develop a program that will continuously monitor a 3rd party website for a specific text string and immediately send notification via SMS to a handful of cell phones when the website is updated to display this text string (no more than 5-10 users will utilize the program, it is for private noncommercial use). The program will ideally function as a kind of web scraper that monitors a website for a specific string of text, and then sends out an immediate text message alert when this text appears. I believe this could be accomplished by a number of means available online, but most custom RSS feeds and scrapers, etc., only update once an hour at best. We are looking to have something that will send notification within no more than a few minutes when the website has been updated with the specific text - something like what WiiAlerts does, I suppose (except we are not scouring the web for Wii's on sale, we just need to be notified when one specific page is updated with a message.) If the turnaround time from the website being updated to receipt of the text message is any more than 3-4 minutes, it will not suit our purposes. We would host the script on our own server, and it should be simple and flexible enough so that on our end a novice user could install the script and make basic manual changes when necessary (the website to be searched, the text string to search for, and the cell phone numbers to send alerts to). We do not need to republish the content or anything like that. Please feel free to contact us if you need additional details. Thank you.