WTB DDR3 Ram

Okay so i have 1 stick of samsung DDR3 4gb. i either want to get another stick of either matching or something that will work with it OR get two matching 4gb sticks. want to spend around 40 or so on the 2x4 or 20ish for the 1x4. Let me know

Or if its an option i could trade my 4gb stick and some cash for 2 4gb sticks.