The one on my CRF was letting water in when I got it and I went on their website and bought a replacement head unit for about £50. Not sure if they still list the head unit as a seperate item now though.
__________________
Caution - the poster may well have been drinking........
Can't see an alternative really. I looked on fleabay for a used unit but no luck.
If you're a real tight-wad you can get a bicycle speedo unit for under a fiver....
I know a CRF 250 rider, not a million miles away from me, who has managed with just that for a few years now. Much cheaper to replace if you smash them.