MAKE SURE they are going to fix the sunroof, those motors/assemblies are pricey and next to impossible to get USED from a yard. But then again west valley has a GREAT deal of 2000+ bonneville parts but the prices on parts are a bit high compared to what they should be .
I'd check the windows, make sure they work. Also test the WOT performance of the car..make sure it has good power and the shifts are firm, check the transmission fluid color and also under the oil fill cap. Also please check the oil pressure after a good hot trip..make sure its not on the low side.
Also point out the hood bubbling problem I believe it has, and also be sure to check for the steering issue, that is the noise it makes when making turns (intermediate steering shaft).
Verify the HUD works and they used a HUD windshield, there should be a dim switch next to the steering column on the left side of it. Make sure it does not have the problems with trunk/door seal leaks a lot of the 2000+ cars have, that is check the rear floor carpet to make sure its not damp. its been cold so it might be frozen and hard to tell if its on the leaky side.
as far as national prices they do vary. $5000 - $9000 is the normal price range for the 2000ish SSEis with similar mileage.
Its possible the leak is caused by an external leak between the LIM gasket and the head, but not very common. its usually internal, thats why I was saying check the oil color and pressure, coolant could have been sitting in the bearings for the past year while its been sitting and rusted stuff out.
overall its a nice car..here are some more pics in case anyone else here had input, bad quality but the car looks nice: