In order to keep the bricky appearance of the train engine intact, [Robert] hollowed out a few cheap imitation LEGO bricks to house the electronics ... which makes it easy to swap the batteries ...
As a general rule of thumb, paying 9p per brick/part is a pretty typical price for Lego. Branded and franchised Lego sets like Star Wars, Disney, Mario, Marvel, and Harry Potter tend to be a bit more ...