This is a remix of my Jabba the Hutt idol. It occurred to me that it's perfect for a piggy bank, and putting the hole for the coins in Jabba's mouth seemed like a no-brainer. Since you probably want to be able to get the coins out at some point, I knew I needed to add a hole in the bottom with a lid, but it was a little challenging. After a couple of tries, I think I arrived at a good solution. Just put a coin in the slot in the lid to screw it on or off.
The model is already hollow, so it's very important that you don't use supports or you might end up with a bank filled with plastic that you can't remove. The entire thing will print just fine without any supports at all. I did get a little bit of stringing around the hole in the bottom, but that is very easily removed. You might also need to slightly clean up the hole in the mouth, but that's it. You do want to use infill, though, since otherwise you will end up with two shells that aren't connected. I used 20% infill and that seemed to work well.
This model can be printed larger, but if you try to go much smaller the hole in the mouth will be too small for larger coins to fit.
If you print this, please post a make! I'd love to see what other people have done.