What is a reasonable estimate for constructing an ADU in LA?

[Bruce P.]

Hi,

A friend is seriously considering building a detached 600 square foot ADU in their backyard in Southern California (specifically the Westlake/Moorpark area in Ventura county). It will have separate metering (electrical, gas, water, etc.) with a private fence to make it "feel" like a private studio.

What is a reasonable contractor estimate for building an ADU including materials and labor? (let's not worry about permits since those are city specific). If it makes the estimate easier, let's say they are not using "top-end" materials (e.g., super fancy granite counter tops) but "solid" (mid-level in price/quality) that give the ADU a modern look and feel and a foundation of materials that would last a fairly long time without being refurbished.

She is getting quotes with a fairly wide range, from $140K all the way up to $190K.

Thanks in advance!