Ronja (Reasonable Optical Near Joint Access) is a free technology project. It uses LEDs to create a 10Mbps optical communication link at distances of up to 1.4km. The system was developed using open source tools and the designs are fully disclosed. Everything you need is on the site: schematics, 3D models, and diagrams. The original systems used visible light, but the current designs use infrared. The parts for building one of these units should cost around $60. It’ll probably take at least seventy man hours to put one together so you’d have to be pretty dedicated to not using commodity wi-fi equipment to go through with this.