Assessing Market Value with high vacancy rate

[Greg Scully]

This is from the MLS

2 ranch style 5 plex buildings on separate lots. Excellent potential. Newer metal roofs in past 10 years, 9 year old boilers and water heaters. 7 units remain vacant, 3 units rented on month to month leases.

The asking price is 450k, comparable rents are around $900.  City appraisal is 360k.  This place needs some rehab to make it marketable.  At 70% vacant this isn't worth much more than the land value.  

Generally speaking, how do you approach making an offer when the marketing package essentially says it has little income and it needs significant work?