The price is very cheap. To store 50 GB of date according to "Standard access storage – infrequent", one pays only $ 0.625 per month at a rate of $ 0.0125 per GB.
Amazon S3 also offers a free AWS usage level where, upon registration, new AWS customers receive 5 GB of standard Amazon S3 storage, 20,000 procurement requests, 2,000 sales requests and 15GB of data transfer each month for a year.
Google Cloud also has a free trial of $ 300 in 6 months.
Using the s3cmd tool, one can set up an automatic cron job to create nightly backups. The script will take a backup of the files of the website and the mysql database and add it to s3 / google cloud and delete the old files.
I have the script and I'm using it for me.