I ride a fancy carbon-fiber road frame for sport but I also commute 38 miles round trip on a Specialized Sirrus with flat bars w/bar ends and 700 x 35 slicks and it's pretty efficient, especially compared to the mountain bike I was riding. I paid $250 for it (used) and it's perfect. I ditched the suspension seatpost and now it's basically a bullet-proof compact road frame with bigger tires and flat bars.