Has a bargain-bin black diamond darkened fiancee Carmen Electra's mood?

Is Carmen Electra's engagment to Rob Patterson already on the rocks, so to speak?

Just a few weeks ago, Carmen was flaunting the black diamond engagement ring the Korn musician gave her at her 36th birthday party.

Now it turns out (sez Life & Style) that he bought her ring for only $1,650 on Mysolitaire.com. Ouch!

"She seems really embarrassed," the insider tells the mag. "I think the ring is a real deal breaker. She thought she'd be getting this giant rock. Instead, Rob bought it online for a bargain price!"

Same insider is saying the duo won't make it to the altar. "He's a total freeloader. Carmen's starting to realize that Rob may not be able to hold up his end of the bargain."

If she goes through with it, this would be a mistake. I mean, marriage No. 3 for Carmen, who was previously wedded to rocker Dave Navarro and Dennis Rodman, for about five minutes.

Perhaps an appropriate wedding gift would be a copy of "Smart Women, Foolish Choices."

Photo: WireImage