Here’s the situation:Purchase Price: $540,000Down Payment: 20%Mortgage Rate: 7.125% (30-year fixed)Monthly Expenses (Mortgage, HOA, Taxes, Insurance): $3,706Realistic Max Rent: $3,000As you can see, I’m currently short $706/month even with max rent.

There are HELOC and 2nd loan options that might work for this property.

Do 80/90% of land 100% of construction loans exist?

Hire a loan servicer - plenty of discussion and recommendation on BP on this topic and some recommendations for servicing companies 

The lots are owned free and clear so the loan would only be for the construction.

Be sure to explore all around the forums as well as many of the FREE tools that Bigger Pockets provides.I am on the lending side of things and am always happy to hop on a call to discuss loan options that are out there, even if not offered by my resources.

What loan?

Often, I am not able to keep all of my ira funds invested in active loans so I would like to be able to keep the money that is not invested in loans in a liquid "money market" type of fund on a temporary basis.

This would apply to your unit.Your biggest concern with setting the rent should be the near future. 1) Your insurance is guaranteed to go up, probably dramatically.  2) You may get an insurance assessment bill to cover the CA Fair Plan losses.

If so you could run the numbers on taking a loan on the zero-debt property to pay off the other.I'm still unclear on the goals - you've brought a lot of other things into the equation (e.g. paying of high interest debt, STR as personal vacation home, stocks/dividends, etc.).