Why pay $2.50 for a taco when you can get one for $1 at the taco truck? There's a restaurant law that you get what you pay for, and �Por Qu� No? delivers the goods: half a dozen taco choices ($2.50-$3.50), plus quesadillas ($3.50-$6.50) and specials like excellent, delicately fluffed tamales ($5). The tweaks are in the details, like line-caught fish and Carlton Farms pork. One recognizes familiar flavors and textures, but they're startlingly detailed and fully realized. Don't miss taco Tuesdays, when happy-hour prices (like $4 for a fresh margarita) last from open to close. (SL)