How did you buy more rentals without crushing your savings account?

[Masud Khan]

Looking for advice on growing my rental portfolio without crushing my savings account in this market.  I have two rentals, both cash flowing and purchased 3 years ago with 25% down and at the record-low interest rates.  Looking to expand my portfolio of rentals, but minimizing eating into my savings account for a 25% down payment each time.  For those who have successfully moved from 2 properties to a third and fourth property, what strategies worked for you?  A few options I hear (on paper).

1) sell the existing units and 1031 into a larger unit property. This is the advice in every textbook, but hard to stomach in this market because the cash flow is good and interest rates are low on the current property.  I would like to keep those and expand my portfolio.

2) Find a fix and flip with 100% financing, using a HML. Then refi into a 30 year.

3) Achieve 100% financing via a HELOC from equity in the current rentals? Not sure a traditional lender would offer a mortgage on 80% unless I bring 20% down.

Any and all suggestions are welcome!