I have been interested in 3D printing for some time but couldn't justify spending $500 or more just to play. Then I found the Monoprice mini 3D printer through Hackaday. It is a well built low cost printer for $200 and I knew that Monoprice's service was excellent so I bought one, but I found the bed was not very rigid making it hard to level and the bed heater was not powerful enough to heat it beyond around 75 degrees. That is not enough for ABS printing. I have fixed both problems by adding a second "slave" heater bonded under the existing bed. The pictures show the final modified machine and the before and after flatness of the bed. The mod cost me around $15 but if you had to buy everything, the cost would be between $30 and $40.