If an owner of the business cannot afford or won't frivolously spend $5/day on a coffee, he or she won't spend money on a SaaS feature that he or she can get for free. Even if he would, to get $500/mo the SaaS would need to find one hundred of such owners.

If SaaS is to price its service at $100/mo, then people for whom extra $5.00/day is a big deal won't be looking at this service at all, won't be contacting the owner about implementing yet another feature, etc. To get to $500/mo revenue, SaaS would need to find 5 owners.