An idea (maybe too obvious) that comes to mind would be to host people's tests and send alerts when tests fail, then work up a deal with Heroku to offer your web testing service as a plugin. Many of the plugin services have the same type of tiered business model. You could do something like a 30 day trial (or, alternatively, 1 test per day free), then offer services for 50 requests, 500, 1000, etc. I'm not incredibly familiar with how frequently web tests run and how many pages/forms/fields the average project has, so obviously you'd have to tweak those numbers based on what you think will generate the most revenue.