Suggestion on a service to manage user, pricing, plans.

I have a product (developer tool) which is free right now and is being by thousands of developers around the world. Its a chrome extension so I had to do nothing with regards to the user, installation etc, except developing the actual app.

Now I want to introduce paid plans in it but don't want to get into things like database, payment gateways etc. So I am looking for a one-stop solution which gives me user signup/login, plan creation ability, purchasing, payment gateway everything. Note, Chrome store's pricing feature is out of question as the app would be available on other platforms also soon. Any suggestions?