Kane will not come cheap. At his peak, Kane is an 8 figure player and if he can return to that form, he is going to prove to be worth that kind of money. It is nearly certain he will not get a contract that big so he could opt for a short-term deal worth small money with a bunch of cup-related bonuses.
If the Leafs were to move on from an expensive player like William Nylander or TJ Brodie, we could watch them open up the cap space to sign Kane and with Kane, they could become instant cup favorites.