Fastglacier is user-interactive, I don't think that it does scheduled backups. Cloudberry is the only app that I've found for scheduled backups (not a bad thing, it's got quite a slick UI and is dead easy to use).
You might know this already but it's worth mentioning just in case: I'm not sure how the Synology backup works, but it'd be worth checking the retention policy on deleted data... if data is deleted within 90 days from Glacier, then you are charged for the full three months of storage anyway. So if you are storing rapidly changing data that gets deleted out of the vault fairly quickly, your costs could be a bit higher than expected.
I haven't done a cost estimate for a full restore in case of catastrophic data loss... I just kind of assume that transfer costs are going to be the least of my worries if both my live data and primary backup become unavailable.