Funny that you're bringing Domi up in here.. because in my head if I were the Sabres GM, the two players I'd be aggressively going after with that 8th pick chip that from what it sounds like are available for trade are Rakell and Domi.
I like Domi a lot, and you bring up a valid point about the contract. My thinking was Domi may cost a little more than Rakell because he's a bit younger and has that RFA status.
At the end of the day though, I'm not bothered by Rakell's contract situation at all (UFA in 2 yrs) The $3.78m AAV on Rakell is going to be better than whatever Domi re-signs for I'm assuming, even if it only ends up being a 2 or 3 year bridge deal. And if BUF were to re-sign Domi to a long-term deal, while I'd like the security of locking him in, the AAV will then be much higher than Rakell's.
Domi is my #2 option I'd try and go for after Rakell though, I think he fits what BUF needs very well. If I couldn't get either, I'd probably keep the pick and draft either Holtz or Lundell.