Welcome to hitched.com.au and congrats on your engagement!
You and your hubby to be need to sit down and go through your budget and how many guests you want, then once you're decided on that speak to your venue to see what you can book around the date you want. You may be able to negotiate in terms of cost, by having a weekday wedding, changing the catering options, using your own entertainment etc. If you explain the budget you have, they may be able to work with you.
The sooner you book your venue, the sooner you can get on with booking all your other suppliers!