Check on the transmission for a round gear with a plug and wires. I think they are electrically operated at this time.
http://www.ebay.com/ has numerous speedometer clusters for $50.00 and under. The unit on the transmission try Ford parts department. Pull the electrical connection and put an ohm meter on it. The ohm reading should go from zero to one. Put the car on 4 jack stands and run about 5 mpg for the test.
If by chance it has a cable look on the transmission also near the drive axle.