“It’s going to be essentially the same as Azure — there’s no upfront fee. It’s a pay-as-you-go model,” said Julia White, corporate vice president for Microsoft’s cloud business, in an interview with GeekWire. “As you use the services in Azure Stack, the meters would spin just like you were using Azure in the public cloud.”
"The prices will be lower than those for the Azure public cloud, reflecting the fact that customers are running their own servers, explained Jeffrey Snover,Microsoft Enterprise Cloud Group technical fellow"
Microsoft's 'Azure Stack' for on-premises servers will use pay-as-you-go cloud pricing model - GeekWire
