The cheapest option is to get a SAS pcie card and a new drive like https://www.ebay.com/itm/198052084090 or try a much cheaper used drive.

LTO drives are expensive but they are very well designed and it is the most reliable portable storage format available. Full LTO tapes in a good fire rated safe really provide a fantastic sense of security. The cost of the drive is amortized over the total bytes you store.