We are going to launch a service that will require between 1 and 2 GB for file storage per paid user. I am going to use GridFS for storing files.

I am pondering the different options for storing the database.

But since I am unexperienced at deployment and it is my first time with Mongodb I need your experience.

Criteria:

• I want to spend my time developing my core business, that is, my own application. I am a Ruby on Rails developer. I do not like to mess with server configuration. Hence, I would like a fully managed hosting solution. But I would like to know about any other option, if you think it is worth it.
• It should be able to scale. Cloud style. Pay as you go.
• The lower the price, the better.

So far I known of these services:

• https://mongohq.com/pricing
• https://mongomachine.com/pricing
• https://mongolab.com/about/pricing/
• http://cloudcontrol.com/add-ons/mongodb/

And they seem to be OK for common needs, that is no file storage. But I am going to use GridFS, so the size matters. These services seems to scale, in price, quite poorly.

MongoHQ: The larger plan max storage is 20 GB. Seems like a very little storage, for GridFS.

MongoMachine: Flat price, 2.5$ per GB. I didn't found the limit. Seems like a good price, comparing the others.

MongoLab: 3.984 GB max, which I don't think I will hit, so perfect. 8$ per GB, quite costly.

CloudControl: The larger plan is 20 Gb. The custom service starts at 250€ plus some unspecified charge per GB.

What is your experience with these services? Any downtimes? Other possibilities?