But until the K&T is removed and replaced with Romex, the contractor could only give me a rough estimate of $5K - 10K .Challenge #2: There may be other issues that come up once this is permitted and the City becomes involved.

Best to just use the estimates as a guide and then get in there and do your own work from there.  

I only have two rentals and this is my current formula for annual rent increase for current renters.The greater of 4% or 1/4 the difference between current rent and Zillow Estimate not too exceed California AB 1482 which is capped somewhere between about 7% and 10%A concrete example:Current Rent $2937Zillow Estimate $35924% = $30541/4 Zillow Diff = $31015% base + 6% CPI cap at 10% = $3231In this case the increase would be $3101Note my rentals are EXEMPT from AB 1482 but I do honor this because I believe it is the right thing to do.

If you want to fix the wiring you just have to estimate the cost and negotiate with the owner, or decide if it is worth absorbing that cost. 

You can also use Shipping Containers.I would use ~$25/SQ FT for the pre-fabs (I am NOT quoting you their price, just throwing out a ballpark figure for estimating.)  

Will have an estimate and review tomorrow.

Purchase price - $99,000Rehab estimate - less than $20,000Total invested - $119,000ARV - $170,000I will BRRRR to pull out my entire investment (purchase + rehab costs).Instant equity from day 1.

Fast forward a year and a half and my property is now estimated to be worth $315,000!!

This is an estimate I recently got from a contractor, how accurate does this seem to you all?

@David Pai The AC was old and he did inquire about an upgrade back in 2019 but fell through as he never gave us an estimate from a referral he suggested.