Like JLee, I use a Synology NAS at home (though I have a multi-drive setup at home with redundancy to overcome a local hard drive failure). Portions of that are backed up to Amazon S3; other portions are backed up to Amazon Photos (if you already pay for Prime, Photos is free for photo files and gives you a small amount of non-photo storage for free as well).
The Synology then also provides home directory storage space for users in the house, TimeMachine backup service for computers in the house, and "CloudStation" (which is a personal DropBox workalike, but where I own the data and has no quota). The CloudStation area is part of the backup set, so most of my working files live on my laptop, on the NAS box at home in Cloudstation, on TimeMachine backups on the NAS, and the TimeMachine and Cloudstation areas are additionally backed up to Amazon Web Services S3 service. Photos are on the NAS, some recent ones on the laptop, and backed up in Amazon Photos and on S3.
I do other things on Amazon Web services as well, so I can't say exactly what the backups are costing me, but I am certain it's under $11/mo (as that's my entire S3 bill for the month).