Could be an error, or maybe not. Right now Amazon has a Yongnuo YN-467 listed at $4.52 + 0.50 cents shipping. [Thanks Jamaal] So for just about a grand total of $5.02 cents, you could be walking away with an extra flash. These Yongnuos don't support communication with the cameras as the higher end models, but event photographers normally keep them in Manual Mode, throw a cheap wireless receiver on them and place them around a room. While it lasts... (click here)
Yongnuo YN-467 Flash Speedlite
And remember, if you want to fire them off camera, a cheap set of RF603s should work with these found below (click here)
Yongnuo RF-603 C1 2.4GHz Wireless Flash Trigger/Wireless Shutter Release Tranceiver Kit
[Update] Looks like the first seller is out of stock. Amazon has shifted to another seller with a $70+ dollar price. No news on any cancelled orders (yet).