That was a massive expense for a PC accessory back then, and today that price would be more than enough to get a very fancy wireless ... This first mouse product from Microsoft had an InPort ...

Lenovo 300 Wireless Compact Mouse,1000 DPI Optical sensor, 2.4GHz Wireless Nano USB, 10m range, 3Yr Warranty, 3-button(left,right,scroll) upto 3M left/right clicks, 1Yr battery, Ergonomic ...