Tin whistle
In recent years a number of instrument builders have started lines of "high-end," hand-made whistles, which can cost hundreds of dollars US each — expensive in comparison to cheap whistles, but nevertheless cheaper than most other instruments. These companies are typically either a single individual or a very small group of craftsmen who work closely together. The instruments are distinguished from the inexpensive whistles in that each whistle is individually manufactured and "voiced" by a skilled person rather than made in a factory.
Physics of whistles
A pea whistle is constructionally identical to a 'police whistle' but the chamber contains a small ball, known as the pea but usually a material such as plastic or hard rubber. When blown the pea moves chaotically in the chamber, interrupting and modulating the airflow to create a typical warbling/shrieking effect. Such whistles are traditionally used by association football referees and those of other games.