34 Approximate Costs for a Foundation The suggested costs for concrete foundations are ballpark prices only given the range of labor and material costs. These really can vary quite widely. You should always ask for a comprehensive quote based on site inspection as certain conditions can greatly affect cost such as slope, ground quality, presence of moisture, rocks, etc. Approximate Foundation Costs * 8 x12 Pressure Treated Wood (1 row on grass or concrete pad, gravel and pavers) ..........................................................................................................................$600–$800 * 8 x12 Slab (2 yards of concrete)....................................................................$1,500–$2,500 * 8 x12 Perimeter Foundation (2-4 yards of concrete)............................ $2,000–$3,000 * 16 x20 Pressure Treated Wood (1 row on grass or concrete pad, gravel and pavers) ........................................................................................................................$800–$1,000 * 16 x20 Foundation (4-5 yards of concrete based on frost level)..........$2,500–$3,000 * 16 x20 Slab (6 yards of concrete). ................................................................. $3,000–$4,500 Many greenhouse gardeners enjoy the do-it-yourself nature of greenhouse gardening and bring friends and a “can do” attitude to build the foundation and greenhouse. The fruits of your labor will be enjoyed year after year!