A typical tab for two at Chi, the chic sake and sushi bar in the Central West End, can easily total $100. Visit the place between 4 and 6 p.m., however, and the same meal can be had for half the cost. While not every item on Chi's menu is discounted during happy hour, there are enough options to satisfy the snootiest sushi snob and the thriftiest upwardly mobile diner and drinker alike. Specials include buy-one-get-one-free nigiri, half-off single- and double- ingredient rolls (listed on the menu as "thin" and "medium" rolls, respectively) and half-off appetizers. The pricey new-age sushi rolls with multiple ingredients and mayo-based sauce Chi serves up are excluded from the happy-hour list in favor of the dishes at which the kitchen excels: no-frills rolls and straightforward cuts of fresh fish. The drink specials are stellar too, with beer, house sake and martinis all 50 percent off. Try Chi's saketini, a tart, potent mix of Tanqueray gin, sake and vermouth. Then, as you sip it, smile at the couple strolling in at 6:05 p.m.