We all know there’s no such thing as a free lunch, but paying a 27.5 percent vig is crazy.

The Post asked financial expert Mike Moebs to calculate the most expensive ATM transaction from among four big banks — Chase, Bank of America, Wells Fargo and Citi — for a New Yorker looking to withdraw $20 for a midday meal.

The highest price tag? If a Wells Fargo customer uses a Chase ATM, that $20 will cost $5.50 — $2.50 for Wells Fargo’s out-of-network charge, and $3.00 for Chase’s non-customer fee.