With ink printers, the ink cartridges add up quickly. With the 3D printers the spools of plastic look like they cost about $25-30 for 600g. One reviewer said that a 1"x1"x2" Lego piece takes about 15g to print. So 15g is required to print about 2 cubic inches. So divide 600g by 15g and you get 40 units of 2 cubic inches, or 80 cubic inches per spool. The cube root of that means that a $25+ spool of plastic prints a block about 4.3"x4.3"x4.3". That can add up really quick!