cost of renovated versus unrenovated apartments in NYC

[Carrie W.]

I know this is a general question, but we are trying to figure out how to adjust calculations of fair market rents when comparing similar renovated versus unrenovated apartments.  Are there any rough rules of thumb for this, especially in New York City?  We need to make some decisions about the relative value of an unrenovated apartment as a rental, but all the comps we can find are newly renovated...

Thanks in advance for any thoughts/advice!