Some radio loudspeakers should do it...

As I don't know where you are, I can't advise where you might get them, but I have some Ross ones which I bought from Asda (part of Wal-Mart in the UK) a couple of years ago.

Quite simply, there is a transmitter which plugs into an earphone socket, and two battery powered receiver loudspeakers. If you use rechargeable batteries in the speakers, the power supply for the transmitter can be used as a charger - a lead is provided.

If you plug the transmitter into the line-out of the PC sound card, it should work okay... mine does!