SAAQ is Société de l'Assurance Automobile du Québec.
SAQ is Société des Alcools du Québec.
G1G have it pretty nailed-down.
For the price, just check the internet for average price in your area for a comparable car. If the car is older than 10 years, it won't be in the books anymore so SAAQ will likely take your word for the selling price.
It's not a bad idea to make yourself a private contract stating the selling price and the car's condition, honestly mentionning any problems you know about and get the buyer to sign it. This will protect you against recourses on obvious stuff. Also, if the owner doesn't get a mechanical verification on the car at his expense, before he buys it, ensure you mark it down on this contract.
Note that in Québec, you are always responsible for "vices cachés". unless you can prove you had no ideas the problem existed and couldn't expect they would occurs, or unless the buyer could not reasonably expect that problem wouldn't occur for a car in such condition.