If you need a wider app and theme ecosystem and are willing to pay for it: Shopify. Its Basic plan is $39/month with no published sales-volume ceiling either — but card-processing fees are separate from that number, and they are not part of the price compared here.
If your sales are approaching six figures a year and you want processing fees that fall as you grow: BigCommerce. Its plan fee rises with a published yearly-GMV ceiling and the account auto-upgrades once you cross it — but the payment-processing percentage it charges on top declines at each tier, a mechanism none of the other four platforms we checked publish.