Without being able to start the car it's hard to determine what else could be wrong with it. Certainly you can do visual checks for leaks, tire wear or dry rot, and brake condition. Ask the seller if they have any maintenance documents on the car. How long have they had it. Personally, I would think there would not be an underlying other "no start" condition other than the stuck key. You need to factor in the unknown in pricing the car.

Other common failure items that could stop you from driving it home include a bad relay control module, and crankshaft position sensor. However, it would be very unlikely they would also be bad, I carry a spares kit that includes those two items.