There is a sweet spot right now for splitting the duplex into 2 condos for an even higher return: The seller forces even more appreciation by selling 2 units versus the entire duplex, yet the buyer is getting a favorable price for the 1 unit vs single family comps.

Our strategy is to sell one unit and keep the other long term. By doing this, we will be able to :

Payoff 100% of the existing loans, including the rehab- this is the financing I have questions about below.
2X( or more) the rental income of 1 unit with no mortgage vs the 2 units with mortgage. Half the doors, twice the revenue.
Reset the equation on capex: complete rehab; exterior costs now shared by Condo Association
Surplus revenue from sale to add to our cash reserves
No cap gains tax ( we lived in the unit within the last 5 years)

So, now, my overly complicated question for financing the rehab:

I’d like to find the most efficient way to short term fund the rehab ( range 65- 75K)

Option 1:

Borrow against the equity of the duplex- but I am not sure what loan product to pursue here: There is a 1st mortgage and a smaller 2nd. The 2nd has a currently stupid rate. We could roll that into a single loan, plus just enough funds for rehab into a cash out refi, but it seems like throwing money down the drain to pay closing costs on that new loan now, to then turn around and sell in the very near term, paying closing all over again. Is there a product out there that could roll all of this into a single close at time of sale? Am I wasting too much time and energy here on nickels and dimes, and do I just need to get busy with this?

Option 2

HELOC on our primary residence for the rehab only, and leave the duplex loans as is until time of sale and payoff. Advantage: Interest only payments during the short term rehab at decent rates. Disadvantage: Additional risk exposure by involving the primary residence?

Other options?

Personal line of credit ?