Beyond rate, is there any cost difference between the two? 

Are there any resources where you can put your income, purchase price, down payment and credit score and see potential rates and which lenders do it?

How you proceed will depend on a few factors:- financing will depend on your exit strategy - you'll be best off if you can decided the exit plan (LTR, MTR, or STR) before buying- Since you're not employed and living on savings, what is your burn rate and your cash runway?

@Cillian KellyI never do because my rate is 3%.

Also insurance rates are cheaper in SC than FL.

People's debt, tax rates and situations vary greatly. 

The property I've set my sights on is a 9-plex where the owners are willing to carry 70% of the loan at a 5.5% rate for a $1,800,000 building.

I asked about costs/rate/terms and he said "6 percent" interest for 5 years.  

Should they choose to move over a refrigerator, they will continue to owe rent, at the rate we set in the lease until we replace them with another tenant.

Have they bought the rate down?