Encontrei algumas estimativas aproximadas em costhelper.com
Installing/replacing a conventional septic system (including the tank) averages $2,000 -$5,000 in the Midwest, but can be $4,000 -$12,000 or more in areas where materials and labor rates are higher.
Enhanced, engineered or alternative septic systems that use mounds, sand/peat filters, aerobic systems and/or constructed wetlands can cost $10,000 -$20,000 or more, according to the Rhode Island Regional Water Quality Program. These alternative septic systems work better than the conventional approach for sites with high groundwater or slowly/rapidly percolating soil, or near drinking water supplies, wetlands, coastal ponds or other water resources.
The cost of a septic tank alone runs about $500 -$1,800 depending on size (ranging from 300-1,000 gallons) and type. Piping and other needed items adds another $100 -$200 to the total cost of materials.