New Foundation cost for ADU

[Vipul Parikh]

I am trying to put together a cost for ADU in backyard in Fremont , CA . It is 20x40 = 800sqft area on a flat land. Can someone please let me know roughly how much it will cost me to add the foundation. I would like to know the cost for slab or perimeter foundation.

I got a 50k quote from someone on phone  for slab , which sounds too high for a 800 sq ft single story. on a flat piece of land