Alex from C4DI has recently launched his NFire 3D printer on Kickstarter. It's a good looking beast, as you can see. The ideas is that you can easily swap out components and print larger pieces or add a second extruder. The price is very competitive (particularly if you managed to snag one of the early bird offers) and it uses a very nice hot end (the bit that actually extrudes the filament.
Worth a look if you are in the market for a low cost and extensible device.