1992 Mercury Marquis Blue smoke

My vehicle just "Failed" smog inspection because it had visible smoke. No test was actually performed as it is an automatic fail if there is visible smoke. I get good gas mileage, no evidence of oil leak and good pickup. The car runs well but, after the car reaches normal running temperature, it will blow a light puff of blue smoke on startup accelleration. There is no smoke when the vehicle is running cold. If I am at a light for a short period of time there is no visible smoke. If it is a long light, poof, visible light blue smoke. Could you tell me what you thing might be the problem? The car is old but has only 70,000 miles on it. It did spend a lot of time in a garage, not used, in its history. It's my only transporation to work and I have to get it fixed so it will pass inspection. I know it won't be cheap but what is the average cost if it turns out to be seals or gasket.