It's a very hard question to answer.
Firstly, is the price 330k higher or lower than similar comparable properties in the area ?
Offer a lot less than similar comparable properties (if it's too low, it will be rejected, and you can increase your offer little by little until it's accepted). By doing this, you know you wont be paying the developer more than he is willing to accept.
Nobody knows what will happen to the housing market between now and the time the property is finished. The reason is because nobody knows the future (except fortune tellers maybe).
However, I went to a fortune teller today, and it was closed due to unforseen circumstances (get it?).
On AAM I think its against the guidelines to comment on what we think might happen to the housing market in the future. I think it's because there were too many threads, and too many emotive posts about the issue.
When you buy your house, you will face the same reality as everybody who ever bought a house. It may rise in value, it may stagnate, and it may fall in value. Quite simply nobody knows.