I checked a bit, but did not find even a hint of valuation anywhere... Would be interesting to know the deal value.
"Terms of the acquisition were not disclosed but we’re trying to find out. And we’ve also reached out to Amazon for a direct confirmation of the deal."
and
"Cloud9 had raised just over $5 million from investors that included Accel and Balderton..."
https://techcrunch.com/2016/07/14/amazons-aws-buys-cloud9-to...