Did they ever mention how the Cullen's have so much money?

no one knows for sure but carlisle is a doctor and has been one for...an extremely long time. so you can imagine how much money that would bring in alone. but also the fact that they dont have to buy food or anything like that either.

Alice can see the future. I think she might use that for financial gain and I'm sure they've made money from real-estate; they do need to move every few years. The others probably bring in money with their hobbies. but to answer the question; no the books do not say how the cullen's have so much money.

Actually, it does say in the series, when Bella states that money is nothing to the Cullens-they have so much of it due to the fact that they have "years and years of accumulating, and a sister who has an uncannily ability to predict the stock market"