NextWarehouse offers the Sabrent 4-Port USB 2.0 Hub in Black, model no. HB-UMLS for $6.80 with free shipping. Outside of the mentions below, that's the lowest total price we could find by a buck. It's compatible with Windows, Mac, and Linux, and features four USB ports with individual power switches and LED indicator lights.
A couple of close prices: Newegg charges $6.99 with free shipping; Store4PC via Amazon charges the same with free shipping for Prime members.