When I purchased the yellow truck last year, I had thought of how about a yellow school bus? Came across this seller selling the yellow school bus on ebay today (USD90) kinda of expensive, if anyone wants to MOC, it shouldn't be too difficult, get 4 wheels, the yellow bricks and start building! The tiles needed are similiar with the yellow truck.
This US seller is currently selling a couple of vehicles, including DHL transport van, Coca Cola Delivery Truck, and so on.
How many children can squeeze inside the bus? It will be good if there are more seats!