I don't know if this is an option for you, but I use a wired headset mic with my PSR2000. Mine is rather expensive. It's the Crown CM-311A whose price was just dropped at Musiciansfriend.com to $199.

The advantage of the headset is that feedback is minimized as the mic is always kept close to your lips.

The mic is not suitable if your voice volume level varies a lot - if you need to belt it out for the high notes. It's also not suitable if you belch and hiccup a lot during your performance, as your mouth is right there, and unless you turn the mic off, everyone will hear.

Beakybird