The dealers tech connected the computer to the vehicle and could get all the guages to respond with the exception of the engine temperature gauge.
As the temp gauge does not have a unique ground, this data point unfortunately swung the odds greatly in favor of a bad gauge. The fact that the dealer gave such a low quote for labor may indicate that they haven't pulled a gauge panel yet. Of course, the other alternative is that they've done many and are very proficient at it! Just in case, here's some info that might be of some assistance.
1. Start by disconnecting the negative ground cable from the battery (8mm wrench).
2. There are two connectors - one blue and one white up under the dash nearby the steering column (just to the left). The connectors' harnesses "Y" together, so if you find one, you'll find the other. The connectors will pull out toward the passenger side of the car - from left to right, if you will. Once the connectors are out, you will find the harness secured with a "Christmas tree" push connector just a couple of inches above where the harness Y's together. The push connector pulls out toward the front of the car.
3. I think that the dash gauge panel removal is easier with the lower dash panel and knee crush plate removed. If the lower dash is removed, be sure to support it very carefully in the narrow area just above the start button and stereo. DO NOT allow the panel to bend here.
4. Lower the steering column to its lowest position. Place a small towel or shop cloth over the steering column. Using blue painter's tape, tape the binnacle (that's the plastic shroud around the gauge panel and with the switches in the lower side). Tape evenly and try not to get it too thick. Tape the area so that when you slide the gauge panel out, you will not scratch anything. Place tape over the switches. Place tape on the top side of the steering wheel and have a cloth handy to place on the wheel when the gauge panel is most of the way out.
5. Next, remove all of the small torx screws holding the gauge panel in place.
6. You will need to gently work the gauge panel out. The left side will come out first. If you have removed the lower dash panel and knee crush panel, you will be able to get your fingers behind the gauges and help to push them outward toward you. Take your time, and make sure your blue tape is in all of the right places. It may help to push up in the center of the binnacle to provide the gauge panel more room to work forward. Also, make sure that the connectors from underneath aren't getting hung up on anything.
7. With the gauge panel out, place a cloth or towel across the top of the steering wheel and the dash. Lay the panel face down. In this position, you will be able to R&R the faulty gauge. Don't over-tighten the nyloc nuts. Notice that the gauge securing studs are approximately even with the nyloc nuts.
8. IMPORTANT: Before re-installing the gauge panel, look at the opening you will slip the panel into. Notice that there is a metal j-clip on the left side at about the 8 o'clock position. This clip is your enemy! (LOL). Frequently when re-inserting the panel, this clip will be the culprit in your way. If you have the lower dash panel off, you will be able to see this.
9. Carefully work the panel back into place. Slip the right side in first. Be careful when you have to go up and over the switches. Again. pressing up on the center of the binnacle will sometimes help. Work it back into place. As mentioned in the previous step, watch that damn clip on the lower left corner. Sometimes it may be necessary to slide a long straightblade screwdriver in there and re-position this clip. Also, you may need to gently pull on the harness connectors and make sure they are feeding down correctly. Go slow, and take your time. It really does go back!
10. Before re-installing the small dash torx screws, make sure that you can remove all of your blue tape. (This step added from experience!) Avoid over-tightening these screws!
11. Plug the connectors back in and re-install the Christmas tree. Re-install the knee crush panel and lower dash panel if removed earlier.
12. Re-connect the battery.