If you're poor you are not a target customer for any non-essential paid for monthly service.

Counterpoint: https://www.rentawheel.com/

A cost of doing business is one of the most essential expenses there is.

The absurdity of an “essential price”... essential to what, class?

To doing business? Doesn't seem absurd at all. Do you think business should just land in your lap for free without having to spend anything for it? That what seems absurd to me.

"business" is just one mode of industrial production, even in a marketplace. So, essential for business, perhaps, but hardly essential in a general sense.

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.