The advantage of Chris's method is that is probably 20 to 100 times faster than usb 1.1 practically.

it is so fast that any time is just about hard disk write time rather than file transfer time, so like he says it feels like you are working on one system rather than two.

I've got usb 2 external laptop hard disks, which are maybe 10 times faster than usb 1.1 practically, but still take a couple of minutes to transfer some cds worth of data. With usb 1.1 it takes an age in comparison, and usb 1.1 is pretty good compared to older methods.

Your $100 might buy laplink gold with a usb cable included, or you might get the cable separate for say $30 and you could use the direct cable connection built into windows. So the $60 extra you pay for ethernet gets you up to 100 times increase in performance which if you have big hard drives pays for itself many times over in the future in time saved twiddling thumbs waiting. If you only need occasional small backups a cheaper solution is fine.