Unless you’re deliberately operating a not-for-profit (trying to cover expenses and nothing else), value-based pricing generally makes more sense than cost-based - particularly for SaaS where the marginal cost of a new customer is low. Lots more:
https://www.google.com/search?q=value-based+pricing+saasRegarding your exact question, since there’s no average number of customers (denominator) or average total expense (numerator), there’s also no use in an average cost-based price. About as close as one can get is to look at the average gross and net (ie, overall) margin of existing SaaS companies. That’s interesting but not a great way to set prices, since prospective customers don’t know or care. They care what your thing is doing for them and how much that benefit (time savings, pleasure, etc) is worth to them.