I would shop the Propane companies. Here in eastern Ontario it's a very competitive market, we have at least 4 to choose from. I rent my 500 gallon tank for "free" (of course, it's built in to the price of their propane). $750 rental for one tank is steep, considering you can buy a standard 420lb tank outright for $1200. It's just like folks that rent their water heaters...good for the rental company, not so much for the renter.
Shop around, knowing approximately what your annual consumption would be, and compare the rental costs vs propane costs to find the best deal/plan that fits your needs.