Wow, I can't believe some of the prices in the other posts. I built my own central vac system for a fraction of the cost (under $400 for everything). The piping is 2" pvc made for vac systems and the outlets (5) were also purchaced. Total cost was about $85 for those parts. The vacuum itself was made from a 30 gal metal drum with a rubber gasketed top.($8) I mounted a vacuum motor ($75) in the center of the drum top and plumbed the discharge outside The inlet to the drum causes swirling around the drum that centrifuges the dirt out. A foam filter over the vacuum inlet in the drum has to be cleaned every few months. A HVAC solinoid and low voltage transformer ($20) turns it on when you plug in a hose and off when you unplug. The hose and electric beaterbar was under $200. It works great, I (my wife really) have been using it for 14 years.
Andy