I once bought a proprietary dinghy bailer, a blue plastic one. I lost it almost immediately. When its replacement also went walkabout I made my own from a milk carton; it lasted for four years. I’ve made several since.
Bailers are easy to make, definitely not rocket science, as you can see from the picture.
I prefer to use milk cartons because the material is relatively soft and conforms to dips and depressions in the fabric base of the dinghy. For a big boat bilge or hard floor dinghy you might choose a fruit juice carton which is made of sturdier material. There may be other suitable containers from which to fashion your bailer – look under the sink, perhaps.