That comment isn't 100% accurate in several aspects.
Equipment hasn't got to be expensive, the Hydrovane was an ex-railways machine, the airlift pump I made out of plumbing bits, the magnetometer and one of the metal detectors was from a dive club, the other detector was from ebay. Sidescan isn't going to be cheap and the boat is a charter boat that generates enough income to buy it and run it.
If I exclude the boat cost, my rebreather cost more than the rest put together and I bought that 2nd hand!
If the weather was good I could recover the total cost in about 3-5 weeks.
p.s. I even built an ROV for under £200, only goes to 20m but it can save a lot of mucking about when hunting for things.