Not very high. Average for the time was like $50,000. I wouldn't pay more than $85,000 for someone like Caesar. Maybe you could get up to $150,000 from a less discerning customer. Your average noble would be more like $300,000.
I've said before that if Caesar had be born now, he would be an SJW. More precisely, Caesar was a malignant narcissist. It's like a psychopath, except psychopaths are calm and collected whereas narcissists are constantly insecure and twitchy. Caesar was constantly getting himself into trouble; high-functioning psychos are too savvy and cool-headed to fail to protect themselves like that. Caesar was hardly without ability but it was all ruined by his villainous and self-destructive personality.
Caesar came to rule because Rome was irresponsible. They left a big-ass hole in their legal security. In particular big enough for Caesar to walk right through. Caesar wasn't noble, he was merely how Gnon's wrath against Rome manifested.