If everyone has to accept cash, then everyone has the same costs and the point is moot. At any rate, courts are required to accept legal tender, and I think that requirement ought to extend to businesses as well.

The real problem for those businesses is way upstream of payment processing costs, namely in the cost of business loans, the general poverty of the American consumer, and (for brick-and-mortars) zoning. The latter is a matter of getting municipalities to relax restrictions put in place mid-century literally to support segregation, and the former two are a matter of forcing the wealthy to eat the costs of their poor decisions from the last few decades, rather than continuing to allow them to socialize related losses through avenues like scandalously low labor pay vis a vis productivity and various investment/asset market scams (which, through housing and passive retirement investment, they've roped in Boomers and older Gen-Xers).

If you wish to make an apple pie shop from scratch, you must first invent an economy that isn't hamstrung by legacy obligations from ventures that people who are long-dead somehow were allowed to finance with your paycheck. (Somewhere, a middle-aged nepo-baby is clutching her pearls at the thought, and I just think we should cherish, rather than shy from, the opportunity to throw her and her siblings under the bus.)