Google Cloud Storage offers multiple storage classes, including Multi-Regional, Regional, Nearline and Coldline.
Coldline storage is probably the best choice for your Arq backup data. But if you expect to restore data often, Nearline might be a bit cheaper.
Nearline and Coldline storage "are intended for infrequently accessed data". In addition to normal data transfer charges ($.12 per GB for data transfer out in most destinations), you incur $.01 per GB for reading Nearline storage data, and $.05 per GB for reading Coldline storage data. Nearline data deleted in less than 30 days incurs a minimum 30-day charge. Coldline data deleted in less than 90 days incurs a minimum 90-day charge.
"Standard" storage comes in 2 flavors -- regional and multi-regional. Multi-regional storage is geo-redundant and is a bit more expensive.
If you choose a multi-region location but coldline or nearline storage class, Google will store the data in one of the regions that make up the multi-region location.
Full bucket location details are here: https://cloud.google.com/storage/docs/bucket-locations
Full pricing details are here: https://cloud.google.com/storage/pricing