Not much initially, prices are dropping slowly now, the sempron for example has been coming down in price by about $5 per week lately, they will bottom out pretty soon, and probably stay roughly the same in price at that point until the production runs on singlecores ends, then they should drop in price by quite a bit.With the amount of computing power the current high end single cores have though I wouldnt look for them to ever get real real cheap to begin with even after they are no longer made.I'd look for intel single cores to drop in price alot more depending on how intel phases out their production,although intel hasnt been known to be all that tough to compete with in the bang for the $$ area like AMD has,so they may keep prices high by phasing out single cores slowly while AMD will likely just quit making them all at once.
OTOH I think we are going to see serious price drops in other things, memory is getting ridiculously cheap these days, LCD's are going to get that way soon too.