Not familiar with the prices in your area, - - but that sounds cheap, - - mainly because the square footage is so small, - - unless every deck is exactly the same, - - or similar, - - either way you need to find out the details first. Generally speaking, - - the posts would sit on concrete piers. Pre-cut stringers can only work if you're going to base the height of the deck on a multiple of the stringer risers, - - that's a rarity.