Looking for a speed sensor for my Eagle Fishmark 480

Trying to get get a speed reading on my old boat...I have a speedometer guage and all I need is a pitot tube and the hose. I can get one of those for less than $20. But wouldnt mind getting a digital reading on my dash mounted Eagle Fishmark 480. The Model # for the sensor is ST-U 99-76.... figured Id cast a line to you guys and see if I could get any bites. Maybe somebody had an old one they dont need anymore. If you do let me know what youd want for it!~ Thanks!

Chris