After looking at variety of options for hosting MongoDB; it seems that Digital Ocean at $20/month is quite bit better than the alternatives; coupled with the free admin interface of MongoLab. Reasoning is in the sections bellow.
Typically my defacto choice is AWS-EC2; but in this case Digital Ocean seems like a better alternative. MongoDB does seem to work a lot better on SSD (ref); hence that is one of the requirements that I had; as well as at least 2 cores.
MongoDB provides preconfigured AMI on EC2 link; however none of them use SSD but instead rely on EBS (which was reported being somewhat slow for mongo (ref)). Even without the SSD the cheapest machine on which AMI could be deployed is m1.large at $144/month. On the other hand the cost of DigitalOcean was just $20/month (7x difference).
Finally; MongoLab kindly provides their nice admin interface for even self-hosted instances.
|limitations||8GB max for “inexpensive” shared instances; dedicated instances starting from $200/month|