There is a hex key bolt near the base of the snout. I cannot remember if it is under the Supercharger engine cover or if it sticks out. The oil should be just barely touching the bottom of the threads on the hex bolt. Make sure the car is cool before checking. The Supercharger takes a special oil which you can purchase at a GM dealer. Pontiac and Buick dealerships should have it in stock. It takes 2 2oz. bottles and in the US I believe they are $6 - $7 a bottle. I actually changed mine altogether just to be safe. I took 1 of my old Armor All bottles and took the sprayer head and tube out and stuck it into the supercharger oil and sprayed it out. It took awhile to get it mostly drained but I just wanted to make sure it was clean oil in it. Be careful with the oil because it is made of animal fats so it smells worse than any oil you will ever smell. It is disgusting smelling but it works.
I am not sure of pricing but I have seen 96 - 97 Boneville SSEi'* from $8,000 - $13,000 depending on mileage and shape. Last year I paid $13,000 for mine but it is fully loaded and only had 39,000 miles on it. Hope this helps.