The issue isn't grades or hills, it is basic safety and compliance with state laws. Find a site like State Towing Laws
(this seems to be offline or gone but surely there are other compendiums that you can find) to see the requirements. Usually it is when the trailer is 3000 lb or more that brakes are required.
$300 for a load leveling hitch is awfully high. For an Equal-i-zer brand that might be reasonable for used but for the typical Reese or EAZ Lift it seems way out of line.