I’m considering refinancing to lower my monthly payment to around $850 and potentially using $30k-40k to invest in one of several ways.

Using a lower-cost skip tracing service and then a call/mail/sms campaign service separately may reduce your costs.

For one, the rental income tends to be lower than with short-term stays due to the necessary discounts, yet we still face most of the usual costs, aside from savings on cleaning and supplies.

There is always a chance that rates will drop, but I would imagine $25K would buy down the annual rate so significantly that you would never see a lower rate offered by a bank so you wouldn't even think about refinancing.

For example, if their lender drags things out and ends up offering mortgage conditions that are wildly different than what we have discussed then I would be forced to accept those conditions or lose $50k.I have also asked if they could lower their earnest money deposit demand to something more reasonable, which they have refused.

That will keep your holding costs lower.

Full construction costs I dont always get relayed to me by the developer, but we were significantly lower than even 1 million on the LS. 

I just put two long-term rental properties on the market that we rehabbed in desirable area of West End Boise and demand is a little lower than expected.

The lower in Class you go, the higher the risk!

If anything I would consider paying down #3 by $75k and recast the loan to lower the payment.