Foundation Issues on First Property

[Logan Allec]

I am currently in escrow on a four-unit property "house hack", which will be my first real estate purchase.  The property consists of three buildings: a duplex, a one-bed one-bath, and a small studio.  The foundations on the duplex and the one-bed one-bath look decent enough, but the small studio has some cracks and has a funhouse feel due to drops in the floor.

I had a foundation guy come out and take a look.  He gave me a quote (see below) for $6,000 - $25,000 depending on how good a fix I want with a summary of the problem as follows: "The structure has settled...the measurements indicate a drop that ranges from -1.9" to -0.4", with the average drop at 1.23"...the structure has sustained two severe foundation cracks...there is wall cracking on the inside of the home: cracks in the front room and cracks in the kitchen."

My predicament is that I simply don't think this unit is worth sinking much money into.  The rent is only $675/month, and the tenant of 15 years is perfectly fine with her dilapidated living quarters.  I would much rather put money into the nicer three units than sink $6,000 - $25,000 into the foundation on the all-around crappiest unit, this studio.  Thoughts?  Am I asking for problems down the road by neglecting the foundation?