Boats are been sold at a range of 20 to 30 percent of Book Value typically within the industry.
Typically only older tonnage selling, the market for newer higher value tonnage is virtually non existent I understand. Gulfmark offshores releases a good source of information on the values.
In respect to new build vessels drying up I don't think this is a worry for the moment. Industry wide ultisation is at less than half and new builds are still on order. Many OSV companies are scrambling to get out of new build contracts rather than take delivery.
I think the only thing the industry could do is scrap older boats On mass and its been predicted that this will happen in about a years time, tho it's a hard call for companies to make. It will likely be their banks that make the call to scrap as they are sick of the cold stack fees (typically $US 700 per boat per day).
An older article below, but provides some background on the new boat side of things.