Had the Oilers bought Nurse out this summer it would have cost them $18.4 MM...which is actually only $6.4 MM more than he is being paid this year. They would have given themselves $10 mil in cap space this year, $8 mil next year, then a few years where you are carrying that massive cap hit (followed by a minor $1.5 mil hit for a number of years). Paying an extra $6.4 MM this year could have erased that contract for the purposes of the cup window.
If the calculator I'm looking at is correct I'm actually a little shocked they didn't do that. Those two years of cap savings are massive for a team in a cup window. They get hit with essentially his full cap hit later on of course but the window is now.