Some changes needed to be made like handrails , entrance ramps,  and wide doorways.

the state wide ADU laws allow adding ADUs with minimal requirements/limitations but there still are requirements/limitations.  

However, I'm receiving such a wide variance in prices (from $500,000 - $1,500,000) and it's hard to know where to spend money to unlock the true value of this property.

In terms of monetary cost, it's difficult to give an average amount, as legal fees can vary widely depending on the lawyer you hire, the complexity of the case, and the amount of time involved.

I assume these are single wides.

I'm definitely interested in turnkey -- As I just don't have the experience or passion involved with rehab -- that being said, from a strategy perspective, I do love the idea of growing a wide portfolio of cash cows in the midwest. 

This can vary widely by region, time of year, quality of work expected, and thousands of other reasons.

Our current market is wide open for long term ownership with turn key properties!

It seems like it’s wide open as the seller is pretty anxious.

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