Desktop application to check an url and then run a script

I need a desktop application that will load and check data on a specified url (I must be able to alter this) I must be able to start and stop the application from running, so maybe some buttons for this. The application will check the specified url, and look for a certain code or certain text on that page. (It would be fantastic if the application was made so i can alter this should the page i am checking changes in the future) It should continiously keep checking this page as fast as possible until it sees the change or the selected text. Once the application see's the code or text appear on that url, it should be able to call an external page where i need a very simple script to send an email (if its php i can do this my self, but id like to use something quicker than php!!!) Once the above has happened, the script should manually stop running. I need this to operate as FAST as possible, so i need the cleanest / fastest language to do the job. I would also if possible (so long as it doesnt slow the application down, show how fast the checks are in real time) I have previously had a script like this made before, but since the url i check has changed so it no longer reads the part i need! I can show this to the bidder so they have a better understanding of what i require! But please no silly bids, the last coder created this for me for $30 and it worked a treat! so i am hoping for around the same!!!!