A large 3D printer is not a terribly complex thing to build. The BOM cost for something like this could be as low as $5000. For some inspiration, look at the Part Daddy from SeeMecnc.
http://3dprinteros.com/wp-content/up...Faire-2014.jpg They use aluminum t-slot extrusion for their linear rails and have an arduino controlling NEMA 34 Stepper motors for motion control. Toss in some SSR's for temperature control of the extruder and you have most of the parts.