Let's see if I have this correct?
You want to create a web-based portal to a db engine1, that has user management2, a queryable interface2 with a free-form syntax-highlighting and handy error-correction providing edit field4, that displays results neatly to an on-screen grid5, and you want to manage6 the user's monthly subscriptions7 and you think it should be fairly simple, easy and above all cheap, and that we're all just sitting on a solution but we won't tell anyone because it's fun to laugh at the misfortune of others ...
Does that about sum things up the way you see them?
While I can point you at several disparate parts (user management and logins are built into the ASP.NET package, you can find a database display and query tool with syntax highlighting as one of the "free give-backs" that the SE team maintains on ... iirc code.google.com, and you can see some other examples in the form of SqlFiddle), I can't provide you with any single resource that adequately does what you need.
Additionally, I want you to assume you're good enough you can tie all the disparate components together, excepting the payment aspect: Each of those numbers above is a minimum of 2 weeks, full time work, for a single developer. Those are MINIMUMS. It would take you 3 months to get most of this stood up bug-free, and that's without an automated clearinghouse for credit-card billing.
Additionally, $2-3/mo is rather cheap ...
In all fairness, this question is neither relevant to this site (read the faq) nor is it an objective question that can be answered with a definitive solution.