Saints are trying to fend off interest in Louis Picamoles from Montpellier, owned by billionaire Mohed Altrad.
Hewitt said players' salaries had shown a "real hike" in recent years.
"Rugby is dominated by some really wealthy billionaire owners in France and the UK. It's becoming a bit like soccer," he added.
"This year we've noticed a real hike in the player salary inflation that's gone into our figures and made our trading slightly more difficult - but that's the way of the world.
"We've just got to adjust to it. We're appointing a new chief executive, it's the right time for me to hand over the chairmanship to John White, who is very experienced, so I think we're well positioned moving forward."
France number eight Picamoles joined Saints from Top 14 side Toulouse last summer and has been hugely influential for a side currently seventh in the Premiership.
The 31-year-old's performances have led to him being nominated for the Rugby Players' Association player of the year award.
But reports suggest Montpellier, Picamoles' first club, are interested in giving him a central contract with the French Rugby Federation (FFR).
"We can't comment on rumours," Hewitt told BBC Radio Northampton. "What we can deal in is facts. Louis has two more years on his contract at Northampton. We love having Louis in the squad.
"He's just won the Saints Supporters' Club player of the season award and we've got an awards dinner on Monday where I'm sure he'll probably get more awards and he's been nominated for some national awards."
The finances in rugby union mean the sport is becoming like football, according to outgoing Northampton Saints chairman Tony Hewitt.