While local prices and soil conditions make this cost variable, we can make a rough estimate. Trenching is approximately $2 per linear foot. Reinforced concrete continuous footings cost another $10 to $15 per linear foot. Add to this about $6 or $7 per line foot for a concrete block foundation wall.Supports in the center may be needed too, but to estimate figure $18 – $24 per linear foot of the parameter.For example if the foundation will be 24 x 30 foot, then you would multiple108 by $18 and then by $24.lab – A concrete slab will cost about $4 per square foot. So if a the slab is 24 x 30 foot, then your slab would cost $2880. This price varies though in different areas, and with the cost of concrete. Crawl Space – The cost is based on the perimeter of the home.