I think it will take way more to dump gardiner

No from buffalo.

There is no reason for the Sabres to do this.

like what

Sam is going to cost more than that

That is a really difficult valuation to make, because there is a lot of term and money left. Realistically, it's going to be 2 B level assets or 1 A level asset. I have my ideas of what that looks like, but I'm not trying to evaluate Carolina's prospect pool. From a pick perspective:
Pick 1-10 = A+
11-20 = A
21-30 = A-
31-40 = B+
41-50 = B
51-60 = B-

from there, it becomes a lot a muddier, as team need, availability and scouting boards change significantly.

A higher draft pick. Look at the Yzerman retention in the David Savard trade. Detroit got a 4th, paid 25% of Savard's cap, and sent an AHL player to Tampa so that Tampa could play a member of Detroit's AHL team. In short, that 4th round pick was worth having a $1 million dollar cap hit on the books, and under $1 million in real dollars.
Gardiner has 2 more years at $4 million paying $8.6m cash. and his Metrics are not great currently. So that draft pick needs to be significantly higher