I did the analysis about 9 months ago for my team when the 980 ti's came out, and the AWS pricing was expensive (we built a server that paid for itself in 2 weeks compared to a g2.8xlarge). This is largely because the 980 ti is actually a ridiculously good deal for price/performance.
The bigger problem we ran into is that AWS instances use a lot of small GPUs, which don't scale well using a lot of deep neural network tools (e.g. theano). It was never really a viable option for us.
The bigger problem we ran into is that AWS instances use a lot of small GPUs, which don't scale well using a lot of deep neural network tools (e.g. theano). It was never really a viable option for us.