Current conservative ARV is 390,000. 

Other more ultra conservative investors may differ so you must first decide if you are one of those or not.

You'll be better served by being more conservative in your analysis.

Use overly conservative estimates. 

I've estimated the full market value of the property to be around $80,000, conservatively.

The other thing to consider is make sure you are being very conservative on the rental income and very liberal on the vacancy and expenses.

I'm having trouble putting a conservative dollar amount on the cost per square foot to use in my calculations before making offers.

Therefore I do not have a set minimum on cash flow but we have never purchased a property with negative cash flow projection but we would consider doing so.Here are two examples of properties that we purchased that cash flow was not a primary consideration:A Duplex that penciled out at about cash flow neutral upon purchase using conservative numbers. 

I have a vacation rental property management business and expect the gross rent on  the property to be $75,000 a year conservatively.

In principle, I agree people should pay for use of water they use as it promotes conservation of a vital resource.