A HELOC is a separate product. It's a home equity line of credit.
If you do a cash-out refinance that will become a mortgage.
You should speak with some lenders about the refi before purchasing the property. Some will have seasoning on the property before basing the refi on ARV vs. the purchase price.
@Michael Weis - some lenders will actually get you as much as 80% depending on the loan program and whether it is recourse (i.e. you personally co-sign for the loan to your legal entity) or non-recourse.
Most traditional lenders have six-month seasoning (i.e. ownership) requirements for you to get refinanced and get your money back out. That being said, I'd encourage you to shoot for a higher ARV so you can get more than what you put in to the property back out via the refinancing.
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