The issue that I am having is that I am not sure how to go about learning how to estimate (a) rehab costs and (b) variable repair and maintenance expenses. 

Also found same issues not being able to get in contact with them.About a month and a half back I got a letter from the county health department about violations with the property.

You are asking someone to sell their house for below market value and they know you are going to make a profit off it, so if you aren't solving an issue of theirs then why would they sell to you?

If it’s a condo, they’re usually pretty easy, older homes have problems, but depending on how you’ve got it set up, you may not run into an issue for months, so paying someone $$$ for nothing kills me. 

My issue is this.

Landlord mentioned 2 issues in reply to deposit - 1.

The damage done to roof with mounting and other insurance issues usually outweighs any positives.Sounds like they have a company exec or hired contractor to call on possible sites and see who they can get cheap rent from. 

No way to estimate the cost until the issue was exposed. 

I'm not seeing absorption rate issues, but really need to sit down with some subject matter experts so I can do a quantitative analysis and 'pitch' with confidence (to investors and banks) before buying our next apartment there.   

I would also run the addresses through the enforcement database and ensure that there is no pending demo order or some other insidious board of health issue.