I know these things are highly variable, but even just a rough example scenario would be helpful to wrap my head around it! 

Variable or fixed?

Is this a mathematical equation, or some other variables to consider before deciding.

You need to know the market you are buying into, but that is just a variable in your underwriting. 

With a complicated enough financial situation, 10 tax accountants will likely have 10 different returns, because not only is one variable how they interpret the code but also how you decide to interpret it, there will be multiple situations where the accountant will advise you on the possibilities of getting an audit, ask you how much risk tolerance you have for the different interpretations of different situations and how likely you would be to pass or fail an audit and warnings that if you fail it you will not only owe the difference in taxes but likely the penalties and interests accrued which could be over multiple years if the return gets pulled years later.

Many of the companies I work with have been using PayLease and are very satisfied with them, especially their onboarding and customer service operations, which appear to be the biggest variables since their fees seem to be in line with the other larger services.

There are too many variables.

Certainly there are requirement variables different in condo financing than in SFRs(owner occupant requirement ratios, current on payment ratios, and so on.), but does anyone believe that now would be a good entry point?  

The lower you go on the economic success scale the more variable and intermittent the borrowers income and thus your expenses putting folks out, refixing the home, and advertising for yet another buyer.The best deal in MH's is owning the park, not the homes.  

For example, your roof estimate of $5000 may be accurate or may be way off, depending on the size of the roof, the pitch, the complexity, the contractors your hire, the time of year, etc.Some of the other prices look in line with what I'd expect, and some are likely way off, but with all the variables involved, it would take a book to discuss all the details of estimating (and then there would still be work that you'd need to do to determine local prices based on the information you had gained).I'm working on putting together a detailed guide on estimating costs, but I'm still a month or two away...hopefully it will help new investors get their heads around all the aspects of renovations and the variables that go into estimation of costs.Until then, I recommend you break all these areas down into labor and materials, and then break your estimates up into those two pieces.