I just purchased a 1984 Honda 750 Magna and the speedometer gave out on me just the other day. I have looked far and wide but very little luck. There seems to be a Honda 500 speedometer for sale but no one can tell me whether the V45(my 750) or the 500 are compatible. Or the 1100(v65). Or previous years or later years.
Would you know about whether there are other speedometers that are compatible, or if not, and I can't get a Honda speedometer, would there be anything else that would be compatible?

I saw some on eBay for large money.

Are you sure the speedo is bad? They usually don't go bad. It's the cable or the sending unit that commonly go bad.