The AWS example is $4 per million char. The starter of this service is $7.92. And the cheapest option is $2 per million which is 2x cheaper, not 8x. Yes the AWS (and google) neural voices are $16 but then the front page voice sampled is not from the neural AWS Polly but standard (Matthew IIRC).
Shady, really shady. It's a shame, I would not mind a good competitor to Polly/Google.