My suggestion would be to let intuition guide your pricing.
That's based on feedback from musicians in the Massachusetts-Rhode Island area who are happy to play at a friend's ceremony for free (or $25 or $50), but quote a price of $2,000 for their band to play at a wedding where they don't really want to be.
An alternative might be to check with a union musician to find out what the prevailing wage is in your area and use that as a benchmark.