It is possible to do it very cost effectively. Just check the newly released product www.nebowireless.com.
In addition to the wireless link mentioned in this web site, which will connect your PC to a dialup ISP via wireless, you need to do the following:
1. Have a network of your two (or several) PCs, either via a router or some type of wireless connection (a cost effective way for the two PCs is the "ad hoc" 802.11 arrangement. Check with any store selling WiFi stuff. Most of salesmen should know this.
2. Use "Internet connection sharing" from Microsoft
Wireless Link just provides a link between one of your PCs and the phone jack. It will be part of the whole setup.
Also try to read the FAQ http://www.nebowireless.com/faq/index.html#q017