Was it another dig at Dumbledore?

It wasn't just a dig, it was a stab. My rereading of the passage leads me to think that Lucius gave that number expressly because of Dumbledore. Remember, Lucius knows that Dumbledore doesn't bargain - and that he gave up on his brother, rather than pay a hundred thousand. Lucius wanted his offer to be rejected, and he was counting on Dumbledore to reject his offer. That explains Lucius's cold smile when he made his offer. And also his confusion, and reassessment, when Harry strong arms Dumbledore into giving assent ... "You pretend you can destroy Azkaban, and Dumbledore pretends to believe it."

It also explains Dumbledore's extremely heavy handed reaction to Harry's decision. The hundred thousand triggered his memory of Aberforth, and to see Harry then choose differently, invalidates Dumbledore's beliefs at some level. Always a painful thing.