A button melodica (or other button instrument) is another possibility. The original Hohner HM-900 (first Piano 26) is an easy choice. It is no longer made, but there are plenty of them around at very reasonable prices, lots on eBay. Look carefully at photos and look to get one in very good condition for under $30.
Although there are no reviews here of this model, it is well known and highly regarded. Sinbce there are lots to choose from, you’d be looking at photos to see a good finish, no chips or discoloration, including at least one mouthpiece, possibly two. If there’s a box in good condition with it, that’s a good sign. There are also the HM-902 alto, and a smaller Student model.