Carbon wheels also jack the price up of a bike as the wheels alone cost $800+. No bike under $1500 is going to come with carbon wheels. Disc brakes, yes. But definitely not carbon wheels. Also, to reiterate wolfchild's post, carbon wheels on what sounds like a commuting/cargo bike is a poor investment. There have been good suggestions above as to which bikes you should look at. Any hybrid bike, Trek FX, Specialized Sirrus, Cannondale Quick will do the job and be within your budget.