Yep, provided Callahan and Filppula were willing to go to a particular destination, the cost will likely be higher to get the team receiving them to take on with no salary relief. The problem with that is that doing it anytime soon severely limits the landing spots because so many teams are set in respect to the cap + they have to be willing to expose another player in the ED. There's only a handful that could take any of these players this early in the season with no salary going back to Tampa or elsewhere. It obviously could be done, but the cost to Tampa may not be worth it. I also can't imagine either of these guys accepting moves to teams not sniffing the playoffs.
As a Devils fan and a team with the ability to absorb some cap, I'd take Coburn provided nothing is going back to Tampa, but the other two I'd be less enthusiastic about. Callahan because of contract length (even though Ive always liked him as a player) and Filppula because I don't think hes a large enough upgrade for $10M over 2 years + both of them need protection in the ED. Lesser in terms of cap relief for Tampa I'd take Sustr, Namestnikov or Palat and be willing to give up mid round picks or lesser prospects for, but I imagine none of those guys Stevie would want to move for relief unless add ons in bigger moves (i.e. Bishop).
Tampa's best move for salary relief remains trading Bishop, since they can at least expect to get something in return for him, but I imagine this is an offseason move unless Vasilevskiy performs at such a high level that he has to be played over Bishop night in and night out. The expansion draft is a wrench that every team has to deal with this season and can't be discounted depending on a particular roster's make up.