If you haven't already bought a printer, you could easily build a large volume printer for much cheaper than the z18 from makerbot costs.
there are plenty of well documented designs on reprap that you could choose from.
http://reprap.org/wiki/RepRap_Options
You could also design your very own! A good design for large build area to look at is an ultimaker, It could give you a good idea of how it is going to work. the design is pretty scale-able.