Sounds about right. An hour diagnosis would cost $110 here where I am and if it only costs about $500 to diagnose and replace the module, that's not bad,,,, Not like it's not a lot of money but those kind of things are expensive.
Find out if there's any warantee coverage on that system. You could call around some other Chrysler specialists and ask for prices and whether it's a pattern failure but usually nobody wants to commit to an answer until they've seen the car.
Here's a directory link for you:
http://repairpal.com/directory?address=72034&car_brand_na...