Estimating rehab in ATL / Atlanta

I am purchasing a property home that was a duplex in the 80s. The home is considered s single family now and cannot be converted back. The old basement unit has plaster walls and the basics. It will be roughly 1200 sqft when finished. What is the best way to estimate cost for this rehab? I would be adding drywall over the existing plaster walls, can lights, a kitchenette and 2 small bathrooms. Nothing custom!