Just take the premium that
you'd be willing to pay and
put it in the bank
In my country, when companies are hired to do overnight rail maintenance, they face very stiff fines if they over-run and delay trains the next morning.
The fines are large enough that (for example) companies will have a heavy plant mechanic on site who does nothing on the vast majority of jobs - they're just standing by, to mitigate the risk of a breakdown leading to such a fine. Some business analyst with a spreadsheet has worked out the heavy plant breakdown rate, the typical resulting delays, the expected fines, and the cost of having the mechanic on standby... and they've worked out it's a good business decision.
The purpose of having an SLA isn't to get yourself money when your provider fails. The purpose is to make costly risk mitigation a rational investment for your suppliers.
