Cost of converting a den to a bedroom in a finished basement

[Emma Brooks]

Hi everybody! We recently purchased a duplex (we are house hacking, it's our first one) and one of the units has a finished basement that is currently being used as a den. A quick Google search didn't come up with anything, so I figured I'd throw my question out here--anybody have a rough estimate on how much this might cost? The basement is below grade and we would for sure have to put in a window. 

Also, we are in a super high demand neighborhood. We are considering making the unit into a five bedroom, as there is the space for it downstairs, and renting it out to college students. I've read other BP posts that say adding bedrooms is only a good way to add value if it brings your unit up to the neighborhood standard (AKA, your property should be approximately the same number of bedrooms as the houses surrounding it). As one of the only multifamily's in the neighborhood, our property is already pretty nonstandard. Making it even more nonstandard is the fact that we currently live in a unit above a detached garage. Should we still try to stick as close to the neighborhood norms as possible, or is our property already so atypical that it's not worth even trying?

Thanks for reading, and I look forward to hearing your thoughts!

Emma