I wanted a simple USB interfaced GPS receiver. I have been using the Trimble Copernicus II receivers for some other projects, so I have software to talk to it and experience with it. I spliced in an FTDI USB to 2 channel UART chip to access the two serial ports out of the receiver. One port provides a standard NMEA data stream and the other provides a proprietary Trimble binary protocol data stream. the 1PPS signal is available through either UART depending on a jumper configuration. The total hardware cost is around $100US per board for the PCB, GPS module and small parts. It took about a weekend of work go capture the schematic and lay out the board. Another weekend of work to build the first board and adapt the simple test software to run on a desktop Linux system (from a Beaglebone).
The project was done because I wanted access to accurate time for amateur radio satellite work. The name Copernicus refers to the GPS receiver and is Copyrighted by Trimble.