While I sympathise with you, are you seriously saying that you are prepared to go to the expense and inconvenience of attending court in Tahiti to challenge this?
15 years ago Europcar in Moorea blatantly ripped me off, but when I got a French Polynesian lawyer involved it was clear that while I might win back my $300 deposit I would incur 100 times more legal costs, and have to stay in French Polynesia to attend court.
The hotel has now formally informed you that a New Years Eve dinner is compulsory (which they can do at any time until you arrive). Your awareness of this condition is posted all over Flyer Talk. You will be giving them your credit card inprint at check-in. How on earth do you think you will get away with not paying?
I first visited Bora Bora as a kid in 1981, when the Hotel Bora Bora was the only place to get a meal. I vividly remember an American couple making a scene in the restaurant when they realised that the only food on offer was a pretty poor set meal (an asparagus, followed by steak, followed by creme caramel) at $100 per head in 1981 money.
French Polynesia is the best destination in the world, but it is expensive. At least there are no tips to pay. But my clear advice to you is to either accept the absurd $300 dinner or rebook somewhere else. (And it would be $200 each if the US economy had been managed differently for the last few years.....!)