Cost will depend on a lot of factors: size of the units, how many head units are needed, how well air sealed and insulated they are, window placement and efficiency, difficulty of electrical and running the lines.

Don't let someone who is in the business of making loans tell you what sized loan you can afford.Find a cash flowing property that you can afford to put 20% down on and start your journey.

Another point is I’ve been in the construction industry most of my adult life so we will be building the home ourselves, saving 10+% on whatever size home we build.

I now realize Turnkey companies come in different shapes and sizes and, to me, it is better to interview the turnkey company itself and find out how they carry themselves directly.

I'll leave an example below that I just had, but seeing that many new folks are looking to start out with a househack, I think this is a good place to just dialog about this particular issue.In the most recent example we saw, we found a home with a sizeable lot, somewhere to the effect of being 4-5 lots in size for the average neighborhood in the area, with potential for just a slight cashflow as-is, but as we saw it, the opportunity to expand by building a detached garage with an apartment over-top that would allow us to keep kosher for owner-occupant with the lender, but up the cashflow for the property by a good estimated $600 a month.

What size projects did you have in mind?

If I have the income and want a house that size, I don't need to say why. 

The problem here is that it is just literally impossible to come up with an accurate number, percentage, or chart for all rental units in all areas.

Get a couple different sizes to make sure you have what you need.

My next step is acquiring financing so I have reached out to different size lenders - credit unions, regional banks, national banks and I seem to be getting the same response back.