Europe still relies heavily on non-European card rails for domestic payments. I assemble a 32-country dataset from central bank and industry sources and use conservative fee assumptions on purpose, to avoid overstating the cost case where country inputs are uneven. Even on that basis, the model indicates about EUR 17.9 billion in yearly merchant acceptance costs, with EUR 13.4 billion linked to Visa/Mastercard-dominated rails. The key uncertainty is whether interoperability and governance choices can align incentives for broad merchant acceptance without recreating comparable fee extraction under a new label.