Cheapest = internet cafe.
This place costs me about 2 1/4 Yuan/hr (although that is a bulk-purchase price, the walk-up rate is 3 Yuan/hr.) I don't know what their link is like but it's good--the few times I've pulled large files they've come in at speeds close to what I'm used to at home and I have the highest tier offered in my area. Most of the machines have exposed USB ports and flash drives work fine in them.