Nothing wrong with cheap moherboards and motherboards with onboard graphics really.
Most motherboards comes with onboard graphics these days, I am actually running on the built in graphics at the moment on this quad-workstation at a rock solid 1920x1200, and if I want to I can connect a second screen to the other display port to run a dual setup.
If you run into a conflict with a graphics board then you can disable the IGP in the Bios.
My vote is for a dual core intel CPU or a second hand AMD CPU (since some of the older ones are so energy efficient and extremely cheap, got my own 3200+ for free), currently my Ubuntu server runs on a 2 GHz AMD and an el cheapo motherboard with integrated graphics, consumes 42 watt idle with 4 spun down hard drives and one 2.5" sys drive running. 35 watts less than my quad workstation with q6600.
