Estimating Repair Costs

[Gage Green]

What is everyone doing to estimate rehab costs? I'm new, I'm learning and one thing I haven't really gotten a grasp on is how to estimate rehab costs. A highly important metric for doing the BRRRR method.

When doing the calculators for estimating cash flow, most properties I put in, after expenses including, pm10%/capex10%/repairs10%/vacancy8%, they normally cash flow anywhere between $100/mo - $300/mo. However that is with a 30-50k rehab with Houses normally 1500 sqft or less, and using the numbers from the rent estimator the BP provides. What Im stuck on is how to get a real ball park number on rehab costs. I don’t know much, I don’t know anything about rehabs and I know prices on materials are way up right now, and honestly I’m just tossing numbers out there. With that being said I’m not getting a real reading on what things cost or real cash flow numbers, in essence I’m just throwing out number “hoping it sticks”. But this is doing me a disservice by not being honest with myself. 

Can anyone suggest any reading or methods on estimating rehab costs please. I am open to any and all suggestions. Please and thank you for your time and info in advance!