I'm offering professional support for an open source product, with the blessings of the team behind it.
What is a good way to structure support to make this good for my clients AND worth my while?
The specific product is the H2 open source database. It's normally used as an embedded database in Java applications, or as a unit-testing replacement for Oracle, etc.
First, talk to you your potential customers (i.e. the current users of the open-source product) and find out answers to the following questions:
With answers to these questions, you'll be able to craft your UVP and figure out the value (not the price) of your service to businesses.
Then you'll know enough to pick your pricing model from the typical ones: flat rate per incident, flat rate for the first X hours then hourly, only hourly, retainer (monthly/semi-annual/annual with/without incident limit).
I think you are best in the early stage of development where the systems of service and suppport are largly being developed and the expectations are only just emerging to make your support the pre-purcahse of time in blocks, billed in defined blocks. Make three purchased time blocks available with increaded value the more time that is purchased. Don't have an expiration on the use of the time. Provide monthly billing on actual time used against their pirchase. The billing block- 15 min, 30 minutes needs to match your market expectation. I think 30 min is reasonable.
The advantage to this is you get prepaid, people are more likely to use time they have purchased, you can build projections of when people will need more. You can throw an hour here or there to paid customers to build satisfaction and loyalty.