That's the issue, it won't be a reasonable cost. Also, if Calgary brings in Duchene, can they still afford to keep Backlund around?
Sooner or later Sakic (or whomever is pulling his strings) will realize that the longer they wait and the more of a distraction this becomes, the more it will negatively affect his trade value. As for whether or not we can afford it, it depends on what the package we give up is. If Brouwer is apart of the deal, then it becomes very possible, if not it becomes much more difficult.
The Flames currently have $58,092,167 tied up in the cap for next season. That's $17,838,290 in space, if the cap doesn't go up and the only major re-signing is Backlund. So let's assume Backlund signs a 6x6 Oilers special and we somehow acquire Duchene and the cap goes up an additional $2 million. The could give us the following line-up with $4,838,290 to fill the holes and with Jankowski, Kulak, F. Hamilton, Gillies and Hathaway as RFAs (that currently look to have a shot at being regulars in 2018-19):
Duchene - Monahan - Gaudreau
Jankowski (RFA) - Backlund - Frolik
Tkachuk - Bennett - Ferland
_______ - Lazar - Brouwer
Hathaway (RFA) - F. Hamilton (RFA)
Giordano - Hamilton
Brodie - Hamonic
Kulak (RFA) - Stone
_______
Smith
Gillies (RFA)
If Jankowski signs for ~$1 million, Hathaway & F. Hamilton for the league minimum $650k and Kulak & Gillies in the ~750k range. That would still leave $1,038,290; this would not be enough to fill the two remaining roster spots. However if Brouwer were moved in the deal, it would be quite easy to make it work, It would even be possible if a little salary as Ferland was included (No, I'm not saying we should trade him).
TL;DR: If we move a minimum of $1.5 million in 2018-19 salary, we could probably make it work.