Last week's letter asked about the role of transaction costs in rationing discounted products, or "sales," like "Dollar Hotdog Night!" at the ballpark.  As the listener correctly pointed out, this relates to price discrimination, which is a great topic. And....coupons! Some additional links and info: The $21 "Dodger Dog" at Chavez RavineThe "Monkey App" kerfuffle in the Bay Area$1 hotdog night at Philadelphia got out of hand, because of course it didRobert Murphy and the Argument FOR CouponsEcontalk discussion of "found wallets" There is no such thing as a free coupon! If you have questions or comments, or want to suggest a future topic, email the show at [email protected] ! You can follow Mike Munger on Twitter at @mungowitz