What do people do for luggage insurance?

[Pearlman]

I was looking at the Baggage rules for Garuda on another thread and came across this: Garuda Baggage Rules

There are specific guidelines that apply to checked baggage that is received damaged, fragile or broken, huge in size, highly valued, or does not match the packing specifications. Such items will be given a limited release label

Wiki says this about “Limited Release Label”:

Under the Warsaw convention all airlines have limited liability for loss, delay or damaged to baggage unless a higher value is declared in advance and additional charges are paid.

So has anyone paid those additional charges after declaring their high value Scuba Gear? What are those charges typically?