I would scan, encrypt and store copies digitally and then keep the physical copies in a fireproof document bag as the cheap option. Otherwise you can speak to banks, they were cheaper than I expected when I researched them but it's still an annual fee and range in cost depending on size and access. There's also private companies which do a similar service.
Item | Current | Lowest | Reviews |
---|---|---|---|
Fireproof Document Bag - 15"X11" Fireproof Safe B… | $29.98 | $29.98 | 4.6/5.0 |
^Item Info | Bot Info | Trigger
I bought this bag for the same reason. I haven't tested it yet though, lol.