Some years ago, Microchip decided to release the firmware and schematics of the PICKit2. Not long after that, the first of countless clones was born.
Many hobbyists stripped down the programmer to the bare essentials. Other commercial variants were made with robust ABS cases and a more secure RJ-12 connector. One version looks more or less exactly like the original from the outside, and it sells today for around 20 dollars!The schematic is viewable at this link. Scroll down to page 81-82, or click on "Appendix B: Schematic"