Propane tank cost versus public gas line

[Stanley Dean]

Hey All- I am deciding on a property in Maryland for rental which is 3 br/3 full bath and noticed the heat furnace and boiler had a gas line. When checking at the back of the house saw the heatpump until might be 2 ton and 2 large size propane tank. So I am trying to rally in my mind the cost of filling these 2 propane tank. I believe they hold maybe 500 gal of propane liquid in each tank or maybe combined not sure. So a 500 gal tank in Maryland home much does it cost on average to refill and for an about 1500 sq ft SFH with no basement how much in average( months) do they last for usage.

I will have to factor the propane liquid usage into the rent since its not metered and u replace the tank when empty.  Also is there an indicator or a method of notification when one can be be aware its time to replace.  What is the turn around time for replacement by the propane distributor.  Does anyone know of a cheap distributor in PG county in Maryland.

Thanks all for the insight.