I use two of these for my USB WIFI internet, works...
**broken link removed**
These have a built in boost converter, and you can connect up to 4 of them together. Not sure how much current is left at the end of the chain, but you could add a powered USB hub on the camera end.
With the maximum of 5 hubs connected with 5m cables and a 5m cable going to your full speed device, this will give you 30m of cable . With a low speed device, you will be able to get a range up to 27m, depending on how long the device's cable is. With a straightforward cable route, you will probably be able to reach out 25m or so from the PC. Simply buy a bunch of hubs and connect them serially with 5m cables