The 30% cut is not a payment process cut or else this would fall under: usury, profiteering, rip-off.
For example, the default price on Stripe (and many others) is 2.9% plus $0.30. For a business with an average order value of $30, that $0.30 adds a full percent, bringing your fees to nearly 4%.
If you do high enough volume, yes, you can negotiate lower prices.