Answer:
If you by a condo, you can deduct your mortgage interests from your gross income, property taxes are also deductible, and you can also get a homestead exemption on your condo since it is your home.
Co-ops on the other hand are corporations that own a building, and you own shares of that corporation. It is very difficult and only under certain circumstances, you can deduct mortgage interest expenses on a co-op, but generally not. You cannot deduct property taxes since you do not own any property yourself and you cannot claim a homestead exemption for a co-op for the same reason.
That is why co-ops are usually cheaper than condos.
