Design/Develop site for users that can each check a URL for changes in content (somewhat like alertra.com)

What I need done: I need a web site that is very simple, yet web 2.0 and user-friendly. The idea is somewhat like an [login to view URL] type site, except what I need is to only monitor a page for a change in the content (specifically the change of one word). The URL pretty much remains the same for all users, its just the variable that the user provides, is what changes within the URL. The web site should have a user login with signup form (email needs to be confirmed by end user, just like most forums). Each user that logs in will be creating an alert. The user will provide a certain variable, and then the site will need to input this variable into a URL that I have provided. The server needs to be setup so that, once the URL is generated with the provided variable, this URL needs to be checked every 1 or 2 minutes for any content changes. (I have the URL ready for you, it just needs to be able to input the user's variables into the URL). The alert will be an HTTP content check, it will need to be able to identify when a certain word in the content has changed. (you cannot set this up as a change in page size, it needs to be able to recognize a specific word). Once the word has changed, a notification/alert needs to be sent out to the user, via SMS or email. The URL check can probably be setup by a cronjob, and needs to check the URL every 1 or 2 minutes. I estimate about 10,000 total users at this time, so this code needs to be designed properly to handle that many requests. I will also be getting a high-end dedicated server, and possibly load balanced if necessary. What I already have versus what the provider will build: I have a Linux Server, and my domain name. You build it and design it. Other context/requirements that providers will need to know: In terms of style, I want something very simple. More like the facebook look, very simple. Nothing too fancy. Web 2.0 style. Specific expertise that I am seeking: Definitely PHP Programming. PHP is what I would prefer, but if you have another other programming suggestions I can take that into consideration. Web 2.0 Design (CSS) is also very importrant. Timeframe for delivery: I need to have it up and running in 2-3 weeks.