The age or type of bottom paint, vessel length and what’s growing down there are all factors that affect pricing. What’s growing down there depends on water temperature, salinity, the density of local underwater flora and fauna, the substrate (what your hull is made of) and how often you use your boat. The location of where your boat is in a Marina or Private Dock can cause unusual growth due to high current, proximity to a leaky septic tank or fertilizer runoff caused by a heavy rain. A professional hull diver will tell you, no cleaning to the same boat is ever the same. A diver will determine what his time is worth and price accordingly. If you are interested in a free cleaning, running aground at your local sandbar is an option.