School busses come in several different sizes too, so you can get the size to suit your budget and number of birds. When they are too far worn out to keep on the road, the school boards sell them cheap. Mine had no brakes, so it had to be towed here. Towing and cleaning and the price of the bus delivered goes 500 to $1000, depending on the size of the bus.
I've had this one since early '08, and it's holding up well. My Hubby made a latch for the door, as the coons were really scratching hard at the "pantry" door, all those yummy birds inside, grin.