Memsql + AMPS have "contact us" pricing unfortunately. Do you know any sharded queue (like amazon sqs,iron-mq) open-source ?
You can have (open-source or free) and develop without community (i think like chrome does that).
The question is: is it worth it ? Without vc-money-cash it's a little hard AND time-consuming.
For open-source fast and clean messaging, I'd recommend NATS, they recently built NATS streaming that builds on top of the pub/sub to include kafka like persistence - http://nats.io/
I don't think nats can be used like I said by looking at the docs.
What are you looking to do? Sharding for what? Data size? Throughput?