This would fit your stated needs:

http://www.ebay.com/itm/Geeetech-Pru...IAAOSwuhhXXlxM

There is a lot of assembly required. Those instructions can be found here:

http://www.geeetech.com/wiki/index.p...ng_instruction

The price is right, they print decent, and when it comes to upgradeability the sky is the limit.