The idea of a small business putting a PR firm on retainer is nuts. It’s just too expensive. For one thing, very few startup budgets have $10K to burn on something that is not actually product or customer acquisition. For another thing, PR firms are notoriously unaccountable. They have a million ways to tell you that they did their job without having any ROI.
So instead of putting a PR firm on retainer, try making your own PR plan with unconventional tactics that allow you to track ROI carefully.