that sounds like a grey area, "you may be charged extra". I would try to find out definately how much $$ and if they would definately charge that fee. It not like they are saying you can't go if you weigh more than 250lbs.
I went to Alaska in 05' and did a helicopter excursion. At the time I was just over that magic number of 250 as well. I had to pay the extra fee, and it was not cheap! It was paying for 1 1/2 excursions because they chrage you for an extra seat. We did the helipcoter over the glaciers and dog sledding. I believe it was just under $500 a person, and I paid close to $700. Very pricey, but well worth it. Once in a life time. It does come down to safety becuase they need to make sure the plane/helicopter is balanced. You will be asked to write down your weight and then the groups will be split up to balance the weight. Pay and enjoy..the safety risk isn't worth any amount of money (although it stinks!!)
Norwegian Star May 2005 (Alaska)
Norwegian Wind September 2006 (Hawaii)
Norwegian Pearl October 2007 (Caribbean, back to back cruises)
Norwegian Dream October 2008 (Bermuda)
Norwegian Spirit September 2009 (Bermuda)
Caribbean Princess May 2010 (Caribbean)
I fly heli's and its very very important weigth and ballance is often the cause of accidents
Intrestingly enought i once had a very serious issue for flying with a passenger who was too light although you can add weights to that side of the heli.
If the weight and blalence are out it might becoume impossable to land as it might be out of the range of controls. Be warned don't lie, its everyone life you risk.
One more intesting fact when you used to check in for concorde they had scales under the mat this saved 1000's of dollars in fuel as they weighed you and ballenced the plane out, every extra lb meant carring 1.5lbs more of fuel.