ASR is available as stand-alone solution or as part of Operations Management Suite.
With stand-alone you pay an initial fee per VM plus charges for storage (replicated data), storage transactions (iops) and outbound data transfer (in case of reprotect/failback).In case of a test- or actual fail over you pay for the running virtual machines in Azure. Operations Management Suite (OMS) includes ASR. OMS is licensed per 2 VMs (standard license) or per 10 VMs (datacenter license). Azure pricing, including a calculator is available on the Azure website: https://azure.microsoft.com/en-us/pricing/details/site-recovery/
Microsoft, Azure Site Recovery/Current, Hyper-V w/ VMM to Azure