I do not know about cheaper, but i believe it may run the same or a little less, depends on how much wall / ceiling needs to be opened and patched to block off the ducts. the 1st floor should be easy to re route to the new unit, so essentially you would be blocking the feed and return to the 3rd floor. the only " new" duct work ( if you can not tap into the old ducts on the 3rd floor) is the new ducts for the 3rd floor. so you would have 2 new units( or 3 if you want to replace the old one) re routing 1st floor feed and return, blocking 3rd floor feed and return and new unit and possibly duct work in the attic. you will get a better system then using multiple mini splits per unit.

If you just patch it up, so the condition is comparable to other properties your repair cost will be lower and then you can multiply with .8 or a bit more.Good luck!

The HOA fee was $200+ a month for a 1 bedroom condo, the property grounds were not well maintained, and they offered NO amenities other than a grassy patch where a pool used to be.  

- Lendinghome- Lima One- Conventus- Patch of land - DoHardMoney.com

But in Somerville we have a 1 bed going for $2500, if they trash that 2500 will do a whole lot more in terms of paying for new painting and patching.

I am a landlord in MA and recently had tenants move out and cause damages to my property (soot all over the walls + holes which required extensive cleaning, patching and re-painting).I did have a security deposit, but unfortunately, I was not aware of the very specific security deposit laws in MA. 

Than a lot of patching and fixing wall cracks and primering the walls.

Get another opinion and do t play hardball with them, bc if you force them into this and they don’t make money you’re going to get a patch job, and since you don’t know anything about plumbing I wouldn’t recommend going that route.

Personally, I focus on having sufficient reserves available to get me thru a soft patch. 

.- Exterior paint, interior paint - HVAC and water heater appear new, roof appears new- Interior has some water stain marks, replace drywall patches- Replace kitchen with modern cabinets, granite, appliances- Oak floors downstairs hopefully can be refinished- Replace carpet upstairs with composite flooring or nice carpet - stairs are carpeted!