Where are you located? Are you located where gold leaves grow on trees?
You should be able to get a good used manifold off www.car-part.com
for under $50. Shop labor at a (RAPE) rate of $75/hr should be about $150. Gaskets can be had from most parts stores for under $15.
You will want to have the replacement manifold checked for cracks by a machine shop prior to installation so they can weld/repair the cracks.... Might as well just have yours welded and save the cost of a replacement.
I am guessing your car is a 92-95 supercharged 3800, correct? If you replace your best bet is to find a low-mileage manifold off a non-supercharged Bonneville. They typically don't produce enough heat to crack the manifolds unless the exhaust is plugged.