Garmin has a flat repair fee, which was $125 for the etrex series, but their website has info on the cost, I don't know if that is the same fee for all their series of GPS units but you'll find out soon enough. It can be haggled though as I managed to get my Vista repaired for $75. You just have to whine enough and say that you know exactly what the problem is and that $125 is a ripoff for a simple repair of the jack.
I begged and pleaded to let me buy the part that I needed (my click stick was broken) and let me fix it myself (I already took my Vista appart to look at the clickstick) and they were refusing to budge, so in the end, they agreed to charge me $75 to fix the stick and to replace the LCD screen which was scratched. (actually they gave me a new unit I think).