Duchene is going to cost more than that, also Hayes will probably cost you a little more as well.

Pretty expensive third line Center, instead of signing Hayes U sign a starting goaltender like a lehner maybe for $5 million and use the last million to get a third line Center, it’s gonna be a great off season though no matter what happens

CBJ also has Kukan on the back line.
Several assets they will probably trade for more draft picks, in addition to Wennberg, would be:
Milano - has fallen down the depth chart, will look to give him a fresh start

(They currently have in order: Jones, Werenski, Murray, Savard, Nutivaara, Kukan, Harrington, Clendening, Gavrikov, and Peeke coming)
I can see definitely trading 2 of the D men above, possibly Murray (injuries), Savard (salary & right side D), Harrington, Kukan or Clendening.
Kukan, Harrington, Clendening, and Gavrikov all looked very good in the playoffs when Murray, Nutivaara, & McQuaid all went down with injury.

Either Lee or Nyquist would be a great signing on the LW, Nyquist could probably be in the $6M range.
I could see Werenski n the $5.5-$6M bridge deal (2-3 year range) to buy time until after Dubois & Anderson are signed.
By next year, Dubi would be bought out and they would lose a player to Seattle expansion.