If you are suggesting that it would be cheaper to buy and move an existing, financially troubled, franchise rather than purchase an expansion team.....the answer is "maybe, maybe not".
At the end of the day you are still dealing with the NHL and need their approval to relocate. Use the failed Balsillie's attempt to buy and move the Coyotes. JB thought he was being smart....offered the then owner far more than the franchise was worth (but less than he would have to pay for a new franchise in Southern Ontario) and made the purchase conditional on getting approval to move. Approval that never came.
If the NHL wanted to fill the Quebec and 2ndGTAteam markets with expansion teams rather than relocated troubled teams they have the power to do that simply by setting the price of relocation + franchise purchase at a total figure that was substantially higher than the price they wanted for an expansion team.
I think expansion is not a great idea....but it is their business, they can control how/if they grow and they can control how/where/if teams move.