What is your rate currently?

In one building I saw rates of $50/night. 

I have found people willing to owner finance their house to me at a lower interest rate.

They can help assess the market value of the property, considering its condition, and suggest the best sales strategy.Direct to Investors or Wholesalers: While 'we buy ugly houses' companies often offer below-market rates (as they typically look for deeply discounted properties), reaching out to local real estate investors or wholesalers could be a worthwhile option.

Preferred returns would even be acceptable but not a straight interest rate play if the lender understands the structure. 

The first question is, can I use a second home mortgage (10% down and lower interest rate) for this. 

@Ben Cochran I hope you have factored STR tax savings into your cashflow and ROI as it can be significant.Leveraging equity to purchase a short-term rental (STR) in Tampa Bay can diversify your portfolio and potentially generate strong cash flow, but it also increases your financial risk.While your properties hold significant equity, adding debt from HELOCs or a DSCR loan could strain your finances if STR performance fluctuates or costs rise.

A quick check of new listings results in many listing that seem well below market rates.   

•Explore private lenders or hard money loans if you need higher leverage, though the interest rates will likely be much higher.

Postcards for example most people hope for 1-3% response rate.