Well - you have a problem, but it's not insurmountable. First of all - is this a cored hull ? If yes - you have a very big problem. Le's be optimistic and go with solid hull.
Before you call anyone - surveyor, boatyard, witchdoctor - you would do well to get rid of the loose piece. The reason I say this is that nobody is going to be able to assess the damage without seeing inside it. If you hire an extremely well-equipped surveyor, he may be able to show up with one of those density meters, and tell you how far the damage goes - but he still won't commit to anything without pulling apart. You might as well spend the two hours and do it yourself as opposed to paying someone else for two hours.
Rather than taking a grinder to it right away, I would suggest you use a spiral saw with a flexible cable attachment - you can buy a Mastercraft one at Sears. You should have one of these anyway - it's like a Dremel with real balls. Use one of the spiral saw bits to cut away the piece that has come loose. Don't go any further.
Now take a really strong flashlight and look long and hard. You are trying to determine if the layers of the hull have separated. Separated, or delaminated, means that there is space between the layers of the roving - not that the gelcoat has come loose. (If there is no roving attached to the piece that is loose, the problem is not a major one.)
Can you stick a screwdriver in between the layers ? Be gentle - don't try to pry them apart - just see if there is any wiggle room at all.
If it has come apart, take a sounding hammer (if you are so equipped) or the handle of a screwdriver and start tapping to see if you can determine how extensive the delamination is. Use masking tape or something to mark the area.
At this point, try to get as much information as you can regarding the structure of the boat - ie: stringers? grid? solid ? hollow? AND THEN call a surveyor. Explain what you have found, and the ask him if he concurs, and - based on the information you have regarding the method of the boat's construction - what other areas should be checked.
If there is actual delamination - I would think that an estimate from the yard for 2K is very low to fix the problem. As you mentioned in an earlier post that they feel it is only gelcoat coming loose, then you should certainly be able to fix it yourself. You will need to sand or grind away an area about 3 to 4 inches around the perimeter of the hole, at a very shallow angle, give the hull time to dry out (VERY, VERY, VERY IMPORTANT) and then use a thickened epoxy or polyester resin to fill.
When you are filling, it is better to use several thin layers rather than one thick one. This makes it easier to avoid air bubbles/voids and gives a better cure.
If this is a cored hull, and if there is delamination - I think you need to see if you can get a second mortgage on your house
Good Luck - let us know what happens!