Based on what the mechanic wrote up, the problem may not be the speed sensor in the hub assembly, but with the wire harness that connects to the sensor. Pull the right front tire and look for a wire going to a connector on the wheel hub (look behind the round plate that has the 5 wheel studs). Follow that wire back to see where it is rubbing on the axle causing it to short out.
If you find the wire has worn through and the conductor is showing, it may be as simple as wrapping the exposed wire. Otherwise, you can cut out the bad section and splice in new wire. Once it is fixed, try to determine some way to keep the wire from rubbing on the spot that caused it to wear through (tie strap it out of the way, wrap some protector around the wire, etc.).
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)