Calculator
A range for a new install on accessible ground, built up from tank, field, excavation, soil evaluation and permits, then adjusted for regional labour.
Poor soil or a high water table usually forces a mound or aerobic system.
Soil and system type, far more than house size. The same three-bedroom house costs one figure on sandy loam with a gravity field, and two to three times that on clay where a mound is the only permitted option.
Get three, and make each one itemise the tank size and material, the absorption area in square feet, the system type, and who pulls the permit. A cheap quote is usually a smaller field or an excluded permit, not a better deal. Ask what happens if rock is hit — a fixed price and an hourly rate are very different bids.