The Oilers issue to my way of thinking is primary scoring, not secondary scoring. One of Draisaitl or RNH plays with McDavid and the other is an island playing with complimentary role players. If they can build a two line attack with another primary scorer, everyone gets bumped back and the onus is no longer on players like Khaira, Puljujarvi and Reider to step up and fit in top-six roles (which hasn't and won't happen).
The dream scenario would be, even if took an egregious overpay, to land Tarasenko. He doesn't have a trade clause, he makes a fair amount but is not overly difficult to fit past this upcoming season. They would need to clear 3.7M or so in 2018-2019 remaining salary for it to work, or else have justification to shut down Andrej Sekera for the remainder of the year.
As for what it would cost to acquire him, I would not move Evan Bouchard and I would only move one of Puljujarvi or Yamamoto. Beyond that I would move any collection of futures including Caleb Jones, Jujhar Khaira, Ethan Bear, Tyler Benson, Cooper Marody on top of the first round pick, suppliment picks and Puljujarvi or Yamamoto.