ARV for the biggest house in the area

[Seth Otto V]

I am currently looking at a 3,100 sq ft house with a 550 sq ft detached garage. I would like to do a live in flip or possibly a BRRR. The problem is, I have no idea how to get a semi-accurate ARV. It's in a sub-urban to semi-rural area and all the houses that are close to it's age (within 30 years) max out around 2000 sq ft. So I don't know how to run comps on it at all and I'm at a loss on how to proceed.

Not needed (?) details:

We're looking at Jefferson County, Missouri

The listing price is 149,900

It needs a lot of work, including a new roof soon and work on supporting the floor.

It's on a septic.