1920's brick rehab costs

[Chris Webb]

Hi all, 

I was wondering if I can get a ballpark number for rehabbing a few 900 sqft apartments in a brick 1920's. My baseline is $15,000, am I off on this price? I know I am not really giving a ton of context, so let me know what questions to answer so I can get to the proper rehab number. 

Thanks!