Crosby is in a class of his own, and one of very few veterans who could be on the move currently; the team that goes after him will need to make a substantial offer.
Rust and Karlsson are definitely more affordable options for the majority of teams looking to add experience and depth to their lineup.
A suggested trade scenario that would send both players to the Wings.
Trade Scenario: Red Wings Ship Nate Danielson To Pittsburgh In Package For Erik Karlsson and Bryan Rust
The Detroit Red Wings Executive Vice-President of Hockey Operations and General Manager Steve Yzerman proved many times in the past that he isn't willing to part ways with young players or sacrifice the future of the team for veterans or heavy contracts.
However, in this scenario, he would add Karlsson with the Pens retaining 35% of his salary, alongside Bryan Rust, in exchange for Nate Danielson, Jonatan Berggren, and a 2028 second-round draft pick:
Detroit Red Wings acquire: Erik Karlsson (35% cap retained) Bryan Rust
Pittsburgh Penguins acquire: Nate Danielson Jonatan Berggren Second-round pick in the 2028 NHL Draft
While it would be surprising to see Yzerman agreeing on such a trade, the idea of seeing two experienced and talented players joining the team next season to help in the playoff push could be enticing.