What about how much money it cost to get whatever currency you had into a cryptocurrency? That may be vanishingly small for people that had BTC cheap and now have a bunch that cost some low initial amount to get into the system, but most people would necessarily have to convert whatever currency they normally have to a crypto currency first and then spend it. A true comparison would compare a few things, including same currency transactions using paypal, differing currency transactions using paypal, cost to use crypto to buy assuming you have none to start with, and cost to use crypto assuming you already have it as crypto at essentially zero cost. And for all those, probably run the number for buying something at $5, $10, $50, $100 and $1000.
Or don't do all that and intuit from it that the likely result is that in some cases crypto wins (when the purchase is large, when the crypto was acquired at closet to zero cost), and in others it doesn't (when the cost is small, or possibly even moderate and when you have to convert to crypto first).
Or don't do all that and intuit from it that the likely result is that in some cases crypto wins (when the purchase is large, when the crypto was acquired at closet to zero cost), and in others it doesn't (when the cost is small, or possibly even moderate and when you have to convert to crypto first).