GUALEGUAYCHÚ, Argentina (AP) — On a recent cross-border shopping trip, four friends from Fray Bentos, Uruguay, visited the nearby Argentine city of Gualeguaychu, where they could afford to live lavishly and snap up eye-popping bargains. Thanks to a huge disparity in the two South American countries’ currencies, Stella Ferreira and a friend treated themselves to a low-cost pampering at a hair salon, while two other friends hunted around for stylish but inexpensive pants. With its economy faltering, Argentina’s peso has plunged against the U.S. dollar and its annual i...