For gourmands, slumming is a $6 burrito at Taqueria Can-Cun. For the rest of us, it's a $2.25 roast pork sandwich at Saigon Sandwiches, easily the best bargain in the city. The clerks start with a crusty roll, fill it with various meats, then add shaved carrots, cilantro, sauce, and lots of mayo. Where's the profit? Who knows? It's simple, hearty food, and one is enough, so get used to spending pocket change. The place also has a vegetarian option with crumbly fried tofu, shaved jalapeño, and lots of cilantro. The store could stand to be about seven times bigger, but that's part of the charm. The counter is piled with odd-looking Vietnamese snacks, which are poorly translated as tricolored rice, pork pyramids, and jellied somethings. A long line is apt to form at any time, but the staffers are quick, heating the sandwiches in three rickety toaster ovens and tying them up in paper and twine. Anywhere else, this would be a $6 sandwich.