Apartment building plumbing nightmare

[Leslie Schwab]

I am under contract for a 12 family that has older plumbing stacks.  We did our inspections yesterday and all the stacks are bad (cracked to various degrees).  This owner is not willing to lower the price so I will be walking away from the deal.  

Could anyone provide some insight for the future on the approximate cost to replace an apartment building stack (3 story) in its entirety?  How much hassle is it to do this when tenants are in place?

I am tempted to say I'll only consider buildings that have updated stacks, but that will eliminate a lot of good possibilities.  Thanks for any other thoughts or advice that I can take into the next deal.