Price for ALL of the stuff should really be no higher than $3,000.
And that price should include:
cost of base plate, wiring/diodes for tail lights, wiring for breakaway, tow bar, braking system, safety cables and the labor to install them all.
Read the manual for the tow bar you buy. Each one has it's own minimum requirements for how low or how high you can be from level.
And yes we all have scraped bottom at one time or another on a real steep driveway. The trick is to look ahead to avoid going up or down one of them. Sometimes there is just an oops. :W