if you can live without 24 bit audio, here's a 16 bit device that is the least expensive audio interface I've found (under $35) :

http://www.musiciansfriend.com/pro-audio/behringer-uphono-ufo202-usb-audio-interface/476149000000000

You can buy them separately at this price, and they also come bundled with a lot of different Behringer products such as mixers

I'm pretty sure there are ASIO drivers available for it. I got one bundled with my Behringer Xenyx mixer. It was easy to set up... just plugged it into a USB port and windows recognized it as an audio interface. It showed up in my list of ins/outs with no hassle.