It's hard to give a definitive answer to this, because everyone acts differently.
Some interviewers would see it as a refreshing and straightforward attempt to avoid "the game", others would see it as an ultimatum or merely an aggressive attempt to "win" the negotiation. This is part of the reason we "play the game" - it's harder to give the wrong impression.
A more usual approach would be to wait until they offer and ask for your requirements, simply to state the same amount and justify it, saying that you've worked out what you currently pay for your lifestyle, how much it would require to achieve that, and that this is the amount for which you would be willing to move.
They may agree to your demands or, if they wish to treat it as a negotiation, they may try to lowball this in the hope of calling your bluff.
Either way, you're in a negotiation whether you like it or not. If they agreed, your excellent negotiation tactic of "be up front about what you want and why" has worked. If they didn't agree, you're now sat there with their offer and your request.
If you're secure in your current position then you can simply state that you're sorry but you value yourself and your lifestyle goals at that level and, while you're appreciative of the opportunity, don't feel that you can accept a lower offer.
The point is that you should expect a negotiation, because it's a) Expected, b) happening whether you want it or not.
At the end of the day, there are two parties at a table who have to find an agreement that works for both of them. Be prepared to either reduce your requirement or walk away, and be aware that your approach may be seen as a hardline negotiation tactic.