I don't have a 3D printer, but from what I've read, try to stay away from any printers that require you to buy special cartridges because right now filament is fairly cheap depending on which kind you use, but cartridges basically allow the company to control what you pay because the printer you have won't work without their cartridges. here is a good website that has various printers and their costs,
http://www.3ders.org/pricecompare/3dprinters/