2-Port SuperSpeed USB 3.0 PCI Express Card with NEC Chipset for $8.99 shipped.  Here is a screenshot for reference.  It is fully compliant with PCI Express Base Specification using NEC Chipset D720200 and has a throughput rate up to 5 Gbps. It also supports simultaneous operation of multiple USB 3.0, USB 2.0 and USB 1.1 devices.  It is a pretty inexpensive and easy way to add USB 3.0 capability to a PC.