I got a Custom Chrome Mini tach off of eBay for about $40 and just installed it this week. The only hard part of the install was routing the tach signal wire back to the ECM. Pin 3 on the ECM is a tach output signal, and you wil lhave to go to the dealer and spend a buck for a pin, part no. 72076-00. If you have the electrical service manual, it is a piece of cake to open up the ECM pin connecter and add one for pin 3.
Here's a link to some more information about this installation:
I think I'm going with the Nostalgic speedometer/tach combo drive. Can get it for a discount from Zanotti's and I know a guy that installed one. He said it was a very simple install, just remove the old speedometer and plug the new one in.
If you want the mileage to be correct on the speedo/tach combo, a dealership needs to send it out to be set. I estimated how much I travel in 4 weeks, added another week. When the combo was returned, the mileage was a little too great. I just rode my old speedo until I reached the mileage and then swapped in the speedo/tach combo.