You aren't their target demographic.
People that do spend money on a cup of fast coffee would realize it's fine for their budget, and associate whatever offer with something affordable.
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.
So this isn't really against the idea, only against using coffee in the analogy.
One of the underlying principles, "Present costs as small pieces, and rewards as a large sum" is important, but there are many other relevant approaches, e.g. free trial, money-back guarantee, etc., etc. Effective marketing usually combines approaches. Analogizing to other small costs can NOT be the whole pricing strategy.
Also, what's a "coffee shop coffee"? Does that mean a place that charges more than $2 for a large?
PS. I don't get the downvotes. Someone who says they won't spend $5 on a coffee because they are poor would be willing to pay for commenting feature on their website?! Something that they could get for free?