For larger sums, I don't see why an individual would need more than a 2-of-3 multisig. Assuming that there is a signing device for each key and a steel backup, this probably maxes out at around $500.

Maybe if you do not have enough secure locations you could rent out a safety deposit box at a bank for one of the keys, which is additional cost of a few hundred dollars a year. But in that case you might as well use a custodian like Nunchuk or something.

People also pay way too much for the fancy steel backups, such as the cassette models with slide-in tiles that retail for around $80 each. A simple plate set where you stamp / etch in the letters is both cheaper and sturdier.