Less than five hours use on this JW Fishers Proton 5 Boat-Towed Marine Magnetometer with all of the extras: 

300 feet of tether cable

CMS-1 Cable Management System with slip rings to make tether handling go smoothly

DDW-1 Depressor Wing to keep the towfish flying low and close to the bottom

UA-3 Altimeter to give you depth readings off the bottom for more accurate placement

MS Surface and built-in LCD screen for heads-up display

$25,654 original price on this complete system that comes in weatherproof, waterproof, Pelican cases that float. Original owner. 

$12,990 USD plus shipping.