The Sydney Roosters have scored themselves a handy set of supporters for Sunday's NRL grand final - the bookies.

Betting agencies say they will lose big money if the favourites, the St George Dragons, win the title decider.

But bookies agree there is still "good money to be made" from the game and the big punters are yet to enter the market.

TAB Sportsbet's Matt Jenkins said the agency has already collected more than $500,000 on the game and expects take in a further $8 million by Sunday night.

He said most of the money so far is trending towards the Roosters, who are considered outsiders.

"The Roosters are an early popular pick firming from $2.40 (Saturday night) into $2.15. Money is running four to one for the boys from Bondi but is expected to even out today," he said.

Mr Jenkins said one smart punter stands to win $51,000 after placing $1500 on the Roosters at $34 in June to win the premiership just before the club went on a five-game winning streak.

Haydn Lane from sportsbet.com.au said the agency "will lose big time", in the vicinity of $250,000, if the Dragons win.

"We'll be barracking for the Roosters for sure," he laughed.

"The big money has been on St George and we expect the big punters to chip in in the last 24 hours prior to the match when a bit more is known about injuries and weather conditions.

"The biggest [bet] we have so far is $100,000 on St George at $1.57, but I think in the next 24 hours we will start to get some really big bets for one side or another."

Mr Jenkins also offered some "value bets" for the game's best player who will be awarded the Clive Churchill medal.

"We expect to take in excess of 30,000 individual bets on this market as punters try to pick who will be the man of the match," he said.

"Dally M Winner Todd Carney is the popular pick and favourite at $5.50, Darius Boyd at $9 seems to be the favourite for many hoping to see a Dragons victory.

"Jeremy Smith was man of the match last week and at $17 is considered value again in the decider.

“A winger has never won the award but we have taken some interesting bets on Roosters flyer Sam Perrett at $67. The biggest bet has only been $150 at $67 but there has been a good sprinkling of smaller bets; maybe a hat-trick would see him collect the award.”

But punters beware - Mr Lane said betting agencies "are usually pretty accurate" when it came predicting a grand final winner.

"More often than not the favourite does get up, it's been mostly that way for us for the past decade," he said.

"But I don't know whether the Dragons are a sure thing at the moment; the Roosters have been the story of the year and no one would be surprised if they got up but if you wanted safe money you would back the Dragons."