An Apple Airport Express can join a wireless network as a client. It will pass the WiFi traffic to the ethernet port for your printer. You can also plug some PC speakers into the Airport to play tunes via AirPlay. Multitasking at its finest.

I have a bunch of the older wall-wart-style Expresses laying around. You may have some, or know someone who does. Be warned that only the 802.11n models will pass WiFi to the ethernet port when in client mode.