I actually just had this happen to me a few weeks ago. I popped a stitch on a purse I bought in 2008. I brought it to the Chanel store and they told me they would not be able to fix it locally because it would be hard to match the thread colour (its pink), especially since it was from 2008 and they probably didn't have the thread anymore. They said they would send it to Paris to be fixed, it would cost $75, and would be returned to me by December or January (at least 2-3 months).
I was very pleased with the price so I sent off my purse. The very next week they phoned and said my purse was ready! I guess they were able to fix it locally after all. I am out of the country right now so my mother picked it up for me, and she said they restitched the entire front flap and it was PERFECTLY done. They also only charged $25!
So $585 sounds extremely steep to me, but I guess it really depends on how bad it is. Here's a picture of my popped stitch before repair, for reference.
Hope that helps, and good luck!