I have now moved a lot of my smaller customers completely to AzureAD (so no onsite AD controllers at all), as part of their Office 365 plan.
Some of the medium sized ones I have moved AD into Amazon AWS. I need thee instances. Two t2.micro's to be the AD controllers, and a third to run Ubuntu and strongswan. I then build a non-Meraki VPN back to the sites.
A t2.micro is maybe USD$3.50 per month. So for maybe usd$11 per month you can have redundant AD controllers in the cloud.