Cheap 15$ mod to expand the z build area of a printrbot from 150mm to 250mm or even higher if you're willing to lengthen the extruder cords.
Go to your average hardware store and purchase 2 3ft 5/16in(8mm)threaded rods and smooth rods for around 10-15$ . Replace the supplied 1ft rods with the longer ones. Optionally lengthen the wires or purchase extensions. Simple, cheap and easy way to add another 6in to your build capability. Be able to print an arm and a leg without paying for one!