Sounds like the Computrainer software where a speed sensor would go from a lead on your rear chainstay to your PC with your bike on a stationary trainer. You would race against your previous best time, visualized as a second bike on the course. Probably less than $200, total, one time expense.*
*I see by 2007 they were selling kits that included the trainers, and that by the end of their run their prices were $1600, but those were definitely NOT the products I had.