2008 Chevy Impala Coolant Leaking

Background: Purchased used 2008 Chevy Impala in August 2009 w/ approx. 25k miles.

Currently at 38k miles.

Having a problem with leaking coolant. It appears to be a slow leak in that we replaced fluid 2-3 weeks ago and only just now had the warning come on the dashboard "Engine hot, turn off AC, idle engine".

We're just 2k miles over the "general" warranty.

Trying to figure out what might be causing the problem and how much we can expect to pay best/worst case scenario based on what the problem might be.

We took it to a family friend who is a mechanic for just a quick look over and he seemed to think more than likely it was a gasket issue and not the pump because he couldn't see anything leaking from the pump.

I want to go into the dealership with as much knowledge as possible so I'm not taken for a ride. Coolant leak seems odd under 40k miles but I'm definitely not a car expert.

So, to the point.

1) Whats the best/worst case scenario?
2) What can I expect to pay?
3) Are there any recalls or TSBs I should be aware of? Tried googling but to no avail.

Thanks so much!