My Nissan 100 nx Speedometer and Mileometer are not working?

Hi there, I hope you can help me?. My Nissan 100NX 1.6 Speedometer and Mileometer just stopped working so no function at all. Someone has guessed at a speedometer sensor
but when I enquired they cost £140 which seems a bit steep to me but if this is not the problem what else could this be?. Hope you can point me in the right direction,Regs Rob