Is this self-serve or are you serving (i.e. portion controlling)?
If you are serving then $1.50 per 6 oz serving is reasonable (considering your cost of goods will support this price). Calculate your total cost of ingredients per serving and multiply by 3 to see if you hit the $1.50/serving price. If this cost is below $0.50 per 6 oz serving then you should be okay.
If it is self-serve then absolutely follow HBMTN & landarc's direction. They will gorge on Mac & Cheese (I will admit that I do