I was looking for a piggy bank to hold my daughter's coins so I made one myself in tinkercad and printed it :)
I modeled two heads for the bank, a classic piggy head and a bunny one, but if you can do basic modeling you can easily design your favorite! (or contact me and I'll try to make it ;) )
For the front window you'll need a piece of plexiglass or other transparent (and a bit rigid) plastic, cut to measure.
For the back opening you'll need 6 6x2mm neodymium magnets.
Also check your printer tolerances, this model is designed with a bit of tolerance for the magnets, the back legs and quite a lot for the back opening.
Lastly the published body is shorter compared to my first print (in the photo): 8.7cm vs 13cm of the old version, since I realized it was WAY too big after printing it.