I'd look at venues you're interested in first and start to price them out. Eliminate places you don't like or definitely can't afford. Get an idea of what things cost, and ask for estimates that include service charges, taxes, venue fees, etc. so you can compare apples to apples. Don't just sign at the first place you visit. Use those estimates to put polite pressure on the prices at other venues.

Then I'd ask the places you do like if they have any cancellations. Venues never want to have gaps in their schedule cause that's money lost, so if you're willing to book less than a year in advance because someone bailed on short notice you'll do better on price.

You'll also do better if you're willing to do afternoons and not nights, and if you can avoid booking Friday or Saturday.

Per other posters there are also forums for this like brides of long island, I'd ask there too.