It's surprising that for what should be one of the most significant days in peoples lives that so many look for the lowest possible price. If you chose your reception venue on that metric, we'd see a lot more weddings at McDonalds.
Prices for a Wedding Celebrant in Sydney can range from $350 (the McDonalds options) to over $2,000 for a quality celebrant providing a unique, personalised ceremony that reflects the couple and is unique to them. The celebrant will know to keep the ceremony, punchy and engaging without making a show of themselves. They'll provide a quality PA. They'll be extremely well organised, but should something unforeseen occur, they'll be unflappable. They'll keep you both present and relaxed during the ceremony.
The ceremony is the heart of the day. Invest well in the ceremony itself and you'll guests will be smiling back at you and really engaged. Cut costs here and they'll be looking at their phone wondering when the drinking can start.
Remember, even if the party is what you're both most excited about, the ceremony sets the tone for the rest of the day.
Good Luck with your big day.