Jakob,
Currently ARM images are available for crunchy software subscription customers only and not available as part of our developer program. We may change this in the future, but at this time we're working closely with customers to ensure a quality experience as this architecture before we explore making more broadly available in the developer portal.
If you'd like to talk with someone on our sales team I'd be happy to connect you so they can get you more details on pricing of ARM64 container builds.
~ Craig