That's 0 seconds per letter, if you're calling out to an existing API, which would be the only way I'd even consider getting into this business. You just take the difference between your marked up rates and the underlying service provider's bulk rates.
Any defensible value in this service is in the marketing/app design, after all. Printing, stuffing envelopes, and dropping them in a bin is always going to be a commodity service.
That's 0 seconds per letter, if you're calling out to an existing API, which would be the only way I'd even consider getting into this business. You just take the difference between your marked up rates and the underlying service provider's bulk rates.
Any defensible value in this service is in the marketing/app design, after all. Printing, stuffing envelopes, and dropping them in a bin is always going to be a commodity service.