I checked D-Link, SMC, and Linksys, the three companies that I think would be most likely to have what you're looking for, and I couldn't find anything. The only think that I've found are USB-to-Ethernet adapters.
Even doing a text specific search of "Ethernet to USB" comes up with the reverse, since some sellers obviously have no sense of direction.
I think you're out of luck on this one. And is wireless USB really
that much cheaper? I mean, would the cost of an adapter + wireless connection still be less than a wireless Ethernet bridge?