I'm interested in building a computer (cheapest parts) that will be the cheapest for mining (not it's solo purpose). I would also be using this as a regular computer, but would like it to be expandible in the near future (expand number of gpu cards). Any suggestions on what graphics cards will go with a good motherboard for the cheapest price? 
You only need to use the high quality ones so that there would be no problem in the future of your business.