Yeh can you tell us where you are planning on getting this ram from? and the specs of it?
Honestly if it is 4gig for $20 its probably going to either:
1. Blow up
2. Not work
3. Not work then blow up
4. Be a piece of plastic with RAM written on the side.
Until you've shown these guys the specs of the ram and manufacturer etc, i wouldnt go and buy it. Really, $20 for 4gig is not something to brag about.