Looks like the door in the second picture is a slider type. I'm guessing that might be more expensive. You can pick up a rv type side door pretty cheap at the rv surplus places. Some framing inside shouldn't cost much.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio