As you can see from the other posts the cost will vary.If you figure about $200 for labor( 2 hours)and 1 hour of diagnostic($100) plus the parts you can be as low as $400.
Do you have to take it to the dealer?NO,but lots of shops are not familiar with the repair and the updated parts to do the repair and they are the only ones that can reflash the PCM which is part of the TSB.
Will you do damage to the car?I can't say for sure,but I have this code showing for near 3 years now with little adverse affects except for really poor fuel mileage and spark plugs fouling due to the computer dumping fuel to make up for the lean fuel reading.
Basically this CEL is caused by unmetered air getting into the intake system after the mass air flow sensor(MAF) most likely a vacuum leak usually caused by the inutile manifold leaking but can be caused by many other things as is the case with my 2000 Windstar,while no one including myself has been able to find the problem.
Personally I would go to the dealer armed with all the information available and see what they say.
As far as your warranty coverage or when it expired only you would know that.Did you buy the car new or used?If new what type of warranty came with the car?If used was it from a dealer or private owner.If dealer what type of warranty came on the car,if private then forget about it.
Good Luck