Create a New Relic Script to check date on field on website

I have a website that has one field that has a date timestamp. The website is authenticated, so the script will have to log in, go to the page that has the date field, grab the date, check if the date is within 30 minutes of the current time, send an alert if it is not. I'd like this to be done through New Relic One, so nothing needs to be installed and running. It doesn't have to be new relic, but it needs to be a hosted solution so I don't have to run any software, and it needs to be an established platform and free or low cost.