The price for the ASI 5810 card averages around $550, depending on which distributor you purchase it from. This is the vendor I purchased mine from, so I know they sell them; http://bgs.cc/catalog/index.php
As for the PC's, it depends on how you configure the computer, you just have to call and spec on out. I believe that company will also purchase and pre-install the ASI card for you if you request it. They build automation PC's for DJB, so they are used to setting one up for use with a professional sound card. I may call them and setup a "recommended" configuration for Stereo Tool.