On average, the profits from such a strategy might be higher in Boulder than all but a select few markets in the country (maybe certain parts of SoCal offer slightly better opportunities?). 

In DC and Boston both, my properties values and my rents double on average every 10 years.

Currently, Syracuse multi-family properties are yielding a 10 cap rate, indicating a strong investment opportunity, while in Binghamton, large multi-family listings average at or below a 7 cap rate.

The average vacancy rate in Austin, TX is currently hovering around 15%.

HELOC would have a higher rate (9's-11's on average) but if you have a specific strategy for it it may make sense.

I agree with @Chris Seveney that you have several advantages over the average rehabber.

There are many areas with high cash flow that experience little to no appreciation, and others that may cash flow a couple hundred per month that have potential of appreciation, though the values of those homes are well below national average. 

OK, that makes two things.Tenants can account for about 40% of a 2-family property owner’s mortgage in Astoria, given average rents and median sale prices.

Mine are in Fort Worth and grand praire, TX with an average price of $800/room.  

Average length of stay is 6-10+ years, another reason vacancy isn’t the issue.