Sounds like the turn signal switch may be bad, if that is the problem then the switch is quite expensive, the switch is from 225.00 to 275.00, I recommend the AC Delco switch, I see two switches listed at RockAuto, so I recommend going to rockauto.com and looking up the turn signal switch, and look at the pics of the 2 AC Delco models they sell, I think the lower ACDELCO Part # D6243D is the one you need, but I am not 100% sure.
Mechanics always mark up the prices a bit, so that part, along with labor sounds about right at the quote given.
I tried to find some DIY videos in case you wanted to save around 175.00, all I could find was a video of the switch being replaced on a Buick Century, I am pretty sure the process to replace it is similar on our PA'*.
The only other thing I can think of that has been known to go bad in PA'* around year is the Flasher unit, the flasher unit is not too expensive, but it is a pain to get to, here is a part number, and a video of a forum member replacing their flasher unit.
ACDELCO Part # 25684395 $29.79