On a whim, I looked into what was available on Newegg. A dual 8-core (total of 16 cores) AMD looks like they start around $1000 for both processors and motherboard combined. Then RAM and case, etc. Two years ago I bought a machine to do some of my first concurrent programming language work, before coming to college. At the time, the only options that didn't cost a fortune got you to about 8 cores, but you had to put up with strange server PCI slots.
It remains to be seen how long AMD and Intel will be able to keep adding cores until their users figure out they don't actually need them. Maybe it'll be like having a car that goes more than 85mph, and how few roads actually let you go beyond that.
Or, we'll actually begin to see killer apps for concurrency on the desktop.