The Belgium international striker joined the Villans on transfer deadline day last summer for £8 million from Genk and has been a revelation in the Premier League over the past few weeks.
Lambert's men are unbeaten in six and the 22-year-old has been a key figure in that run, producing an eye-catching performance against Liverpool at Anfield last weekend.
"I think Christian, since he came here, has been excellent," Lambert told Sky Sports News.
"He was probably unheard of and nobody really knew too much about him.
"Then all of a sudden he's doing what he's doing and then everybody takes notice.
"He's been an absolute steal. Transfer values are ridiculous but I'm pretty sure he's not worth seven to eight million now! I can't speak highly enough of what he's done."The 22-year-old has been linked with a move away from Villa Park in January but Lambert has ruled out any possible transfer for the Belgian.
Benteke has scored eight goals in 17 appearances for the Villans this season, after initially struggling to settle in at the club.