Do you use the same formula for primer and 2nd coat or do you use ex. $1 square ft for each application

I would expect to pay a professional in the $1 ballpark, since you are asking I assume you are not a pro, right? If you are a handyman you need to keep your pricing competitive, more like $ .50 s/f Try this Estimating a Paint Job - Square Foot Price (http://ezinearticles.com/?Estimating-a-Paint-Job---Square-Foot-Price&id=2912866)