i have a china 4" Analogue style,digital speedo that i picked up for $20 off ebay, it works pretty well
uses a magnetic pickup off one of the wheels.
it has speedo, odo, indicators, high beam, ignition on, and led back lighting
i am using it on my sons Dune Buggy.
i posted up a few links to speedo's on Goosemans'
XR600 (click on the highlighted part to view) thread a little while ago too.
some of them were fairly cheap too.
check out posts; #84 and #86 for the ebay links, there might be some others back up the thread a little too?