I have a lot of data backed up, but some of it I am retaining for regulatory requirements and some of it is mission critical. For me the two don’t hold the same value. Is there an option to pay for a backup service based on the value of the data?
Offhanded, I would say "No, not really".
For a backup [software] all your data has the same relevance. That means "file1" will always be as important as "file2".
However some tools and [online] services are able to differentiate priority based on usage. CrashPlan PRO for example is able to prioritize most recently changed files.
My personal advice is to create additional [independent] schedules for your mission critical files. For example you could run a regular incremental backup of all your data every 24h and in addition a full backup of critical files every hour.
My point of view:
It doesn't really matter if features for priority or relevance exists simply because I would never take my chance relying on them. Choosing the right backup strategy is the most important part to secure your files.