a budget PC for learning linux

So I want to build a low budget nearly all parts used pc that will help me learn how to operate on different versions of Linux. I thought of maybe doing a PC that uses DDR3 ram to get good deals on parts that most of the time are sold for a chocolate bar or a bear in my area. I want to know what type of stuff should I look for to make learning linux more enjoyable. Also would Linux work with integrated graphics or do I need to have a GPU of some sort?