DigitalOcean offers a backup service (only for Droplets) which creates a backup per week and retains the last 4 backups. You have to pay 20% of your Droplet plan for it.
By connecting your DigitalOcean account to Weap.io, you will be able to schedule automatic snapshots for both Droplets and Volumes and you will pay 0.05$ per GB per month.
Additionally, you will be able to replicate your Droplet snapshots in multiple DigitalOcean regions at no additional cost. This means that if you replicate a 10GB snapshot to 3 regions, you will still pay only for 10GB, not 30GB.