This is the absolute worst time of year to buy a propane burner, so if nothing else wait to do the costing until after Thanksgiving.
From what I've been told, the BTU/hr ratings are all but meaningless unless you're comparing two burners from the same manufacturer. An actual 100,000 BTU/hr would be massive overkill for home brewing - that would bring 10 gal from room temperature to a boil in <20 min. Unless you're willing to literally burn through propane (and money), you'll never be running it wide open anyway.
You may just need to replace your regulator. I have a Bayou SP10 (probably the same burner with a 20 psi regulator) and it's more than enough for 10 bbl gal batches.