I've been looking for the next project car, and I've decided on a 9C1 (Caprice cop car) but from 94-96 with the LT-1 engine.
$3,500 is a bit high in my area for the car you're looking at. As LibertyStick said, the LT-1's are around $4000. More if you want less miles. You probably won't need the LT-1 equipped top speed of 141mph, and it may be cheaper to fix the old style 350 when it breaks too.
The high mileage is of less a concern than how they were put on. Some things to think about:
Find out what agency owned the car. Highway patrol cars usually are driven by few officers. They also have mostly highway miles on them. They are ususally pretty strict on scheduled maintenance.
City units are usually driven harder. Watch an episode of "Cops" and you'll see the driver with the tranny in "1" everytime he's getting on the gas. Nearly all their miles are stop and go in town. Big city units can be driven by many different officers. They flog the car, then leave it for the next shift to flog some more. Since so many share the same car, nobody bothers to take care of it.
Small towns and many Sheriff's department (jails) have no money and run the cars to death. The car has to die before they'll do anything to it.
If you find out what agency had it, you may be able to get the maintenance records. It may not be worth the trouble, but it might stop you from buying a $3500 car you'll need to spend another $2500 in transmission, engine, suspension repairs.
Get it inspected by a mechanic. It may sound like too much work, but I'll never buy a used car unless an expert looks at it. Some I'm confident in inspecting myself, most modern ones I'll have somebody with all the right stuff look at it. Even if it costs you $100 it's worth it to save that $2500 in hidden repairs.
The tranny is usually the weak link in any police car. The Chevy is no exception. Figure on transmission work unless it's been done already, and done right. Barring abuse, the suspension and the rest of the drive train shouldn't be any worse than any other car with that kind of mileage. The engine will need work sooner or later with that kind of miles, but the 350 isn't going to give you any suprises that you can't fix. You'll have to change all the fluids and flush the cooling system at least when you get the car.
As for price, offer $2500 and settle on $3000. ONLY if it's in good shape. There's no price low enough to buy a money pit. Budget an additonal $1000 from the get go for unforseen repairs. If the car is going to cost you more than $1000/year (or whatever you feel is appropriate) to run it, than it's probably not worth getting. The $1000/year figure is what I use, figured up by adding the purchase price to the maintenance costs for major repairs. Use whatever figure you're comfortable with. example: $3000 (purchase price) + $1000 (tires, tranny, engine, shocks, etc over time) and that's $4000 total cost or four years worth of driving (40,000 miles for me). If I didn't think the car would make it to 170,000 miles I'd have to reconsider the cost. This is an example, just use your own figures.
Good information can be found at several sites. Do a search for police cars or "9C1", which is the GM code for the Caprice police package for all years/body styles it was offered. [url]www.9c1.com[/url] is a great place to start. [url]www.4adrive.com/~9c1/[/url] is another good one.
Ross