@maz_phil as
@waltworks mentioned, HELOCs are not as easy to find on rental properties as they are your primary residence. BUT they are out there.
National banks that perform LOC on investment properties that I've personally worked with over the last 12mo...Huntington (huntington.com) - 80% LTV, paying approx. 7%
NFCU (navyfederal.org) - 80% LTV, paying approx. 6.5%
PenFed (penfed.org) - 80% LTV, I didn't follow through with the LOC but rates run prime +1%.
Your credit unions will probably offer something more competitive with less underwriting - call them and ask to speak with the commercial lending department. I'm seeing 80% LTV at PRIME in Texas.
Some HELOCs have been only drive by appraisals, which range pretty true to Zillow and others have been a full appraisal. But it's a very cheap and effective way to get funds.