How to create 4 editable vocal tracks of our acapella group>

We have an acapella quartet. I want to be able to record each vocal part (Soprano, Alto, Tenor and Bass Parts) and create for each part an editable track. I am fairly literate with the use of audio editing software but am mystified as to how to create the separate tracks without singing the piece four times each time giving the microphone to a different member of the quartet.

Without spending a lot of money (I would like to keep the expense to something under $200) is there a way to accomplish what I wish to do. If so ... How?

You need a 4-channel usb replacement soundcard that can work with 4 separate mics at once.

(be careful, a lot of usb interfaces really only send 2-channels at a time to the computer. You have to look carefully at the specs.)

Somthing like the
Akai EIE (comes with protools software too)
TascamUS600 (comes with Cubase)
or NI Komplete6 or similar.

Now mind you, 4 mics alone will set you back more than $200.
Shure SM-58's aren't a bad start.