My wife is not a shooter. She is not anti-gun by any means as she sees their importance in defense (she has her CCW and did it without me), exercising 2A rights, and she loves venison and wild waterfowl. But she does not enjoy them as hobby like I do, and she thinks that once you have a carry gun, HD weapon, and a gun to hunt with, why do we need more?
But she also respects and loves me, and understands that I enjoy shooting as one of my two hobbies (I am a huge golfer as well, another "not-cheap" hobby).
As such, I have never hidden a single gun purchase from her, or deceived her on how much they cost. I do not seek permission beforehand either. But I am also not sacrificing funds that should be spent elsewhere. If all the bills have been paid at the end of the month and we have put the agreed upon minimum into the various savings accounts/retirement funds/etc., and there is some extra cash left, I will pull some of it aside. After a couple months if I have enough for the gun I want, I will go buy it, or go stock up on reloading components, or go buy that new putter that will finally save my golf game. Conversely, I do not get upset when she comes home with that new handbag or a bottle of wine that costs as much as a surplus Mosin.
We both work hard, and we make pretty much the same amount of money, so money issues are never really an issue for us. We both recognize the need for limited independence from each other, whether that be financial or just time away doing something we enjoy without the other person.
We are expecting our first child in 10 weeks, so I would imagine that a lot of that "disposable income" will be re-allocated, but we plan on the principle not changing. It may take me 6-8 months to save up for a new gun instead of 3, but life is a series of trade-offs, right?
In the end, it comes down to trust. We both know and trust that the other would never do anything that would put us in a precarious situation, and we are open and honest about it at all times.