The most common problem with the gauges seems to be bad solder joints where the connectors behind the instrument cluster mount to the circuit board. This is a problem often seen, and not too hard to fix; if you have a phillips screwdriver, a set of the lilttle torx style wrenches, and own or are willing to buy a small soldering iron. On mine the fuel gauge and the speedometer worked when they felt like it - about half the time. The link below has the details:
http://www.myneonspeed.com/howto/how...clusterfix.htm
This fixed the gauges on our Neon. If you damage the cluster, any cluster from a 96 to 99 Neon from a junkyard should work, after soldering Its connectors. They have prices (here in Texas) varying from $20 to $75 for a used instrument cluster. And they are easy to remove from the car.
Also available on ebay.com now and then; but you still will need to solder the connectors!
Let us know if this doesnt fix the problem.