> How many legitimate transactions are made more expensive, or never begun at all, because of AML regulations?

Vanishingly few, I'd say? You're asking that in a rhetorical sense: "Ah, but you didn't think about this did you? That invalidates your point."

But your question is a real one with a quantitative answer. And in fact AML statutes exist (or don't) in lots of different markets in the real world, and were introduced at different times. You can look at the macroeconomics if you want and try to puzzle out the effect.

And really there is none. Western capitalism was going gangbusters through the whole period in the 20th century where cash flow tracking was being introduced. And contemporary regimes that resisted AML introduction (c.f the famous swiss bank account) really didn't grow any faster or slower.