I don’t know the exact origin of this photo, but all I care about is figuring out how to make one for myself. I am worried that the model pictured is not actually waterproof/aquarium safe since there is no water in the aquarium. Of course I could be wrong, but I have my doubts (probably cardboard/paper construction materials).
I think you could use vinyl decals for the clouds and 2D graphics like a background, but the castle and pipes would need to be made from some kind of plastic or ceramic material. Perhaps if you had a 3D printer you could make a lot of this from plastic, and place decals on the sides like home-made Legos. Even better – maybe you could use Lego blocks! It would be expensive, but so are the other ideas I’ve come up with.
In conclusion, the only ‘cheap’ method of making this would be to use cardboard and paint, which won’t fly in an actual aquatic environment.
I know it’s silly to expound on a topic such as this, but I found it really interesting and I like to analyze. Besides, this is my site. I can do what I want! :p