After my positive experience using an agent and going off the MLS and my negative turnkey experience I really am down on turnkey now.  

 :)For low $$ deals I suggest marketing for low equity nice home sellers then offer lease option or subject to to control the property.  

That additional equity (the 50k) is now in your pocket and freed up for you to invest in the next deal.  

Is the initial negative cash flow ok to overlook knowing I can cover the difference AND that the deal will eventually lead to positive cash flow in excess of $100 each unit per month once I re-finance and move out of one of the units?

It is possible to over pay on the purchase and yet have a high ROI say... 20% with higher cashflow which would make it underpaid in a sense Ex: Home1 50K BELOW market cashflows $400/mo 12%ROI / Home2 100K OVER market cashflows $1000/mo 19%ROI......... just know that your probably not refinancing anytime soon and that equity is off the table for now. 

@julius dixon (HELOC) Home Equity Line of Credit.

You are put in the position of having to accept their title insurance (which frequently includes exceptions) or losing your deposit. 

But a good set of rentals will always provide cash flow, and almost guaranteed equity in 3-5 years (unless you blow the initial deal).   

Now that my first rental is giving me a $500 cash flow I have about 120k in equity as well.  

Im guessing you can only buy tax liens attached to property that has 100% equity?