Valuing a multifamily home in Rockland County, New York

[Calvin Thomas]

Looking to expand my real estate buys and entering Rockland County, NY.  There is a 5 family building for sale.  Actually, it's a four family building along with a detached unit on the same property.  It's been listed for about 150 days.  It's seems about 100k overpriced, however, the rents are pretty nice.  However, the school/property taxes are significant.  I did some searching on valuations on Prop. shark and other sites, but nothing gave me a good price comparison.  

Any ideas on how to proceed?