Someone else has mentioned M-Disc and I want to second that. The benefit of using a storage format like this is that the actual storage media is designed to last a long time, and it is separate from the drive mechanism. This is a very important feature - the data is safe from mechanical, electrical and electronic failure because the storage is independent of the drive. If your drive dies, you can replace it with no risk to the data. Every serious form of archival data storage is the same - the storage media is separate from the reading device.
An M-Disc drive is required to write data, but any DVD or BD drive can read the data. It should be possible to acquire a replacement DVD drive to recover the data from secondary markets (eBay) for a very long time if necessary, even after they’re no longer manufactured.
Hmm… how does one anonymously pay an internet service provider with cash? Mail it in an unmarked envelope, with just your account name? Roll up to the front door and hand it to the receptionist?