Redknapp is willing to take the defender to Fratton Park, but is reluctant to pay over the odds for any player.
"I like him, Kaboul," Redknapp told Sky Sports News.
"He's a young player I tried to sign before and I'm interested, but the price has got to be right.
"We can't be paying over the top, you've got to pay what you consider to be a fair price for players.
"I think clubs, like us, need to do a deal where if you go and play games and they're successful, great, you pay the money.
"If players come and they don't do the business, I think you've got to be more creative with doing transfers.