Im going to share 2 pearls of wisdom with you that will have your wife looking forward to seeing new guns come into the house for the piddly sum of $200 per year. You need to do these in order.
First is achieving "critical mass". Critical mass seems to be around 10 gun for most people. Thats the number of guns you need to have that makes it impossible for your wife to know that a new gun has popped up in the collection.
The second part of the plan is the "$200 per year investment guns and the payoff" plan. When you just cant sneak a new gun into the house, bring it in right in front of her. When she protests, tell her you only bought it because you got it cheap and you're putting it up for sale for more. The payoff is when, about every 6 months, you walk up to her and plant a hundred dollar bill in her hand. When she asks what its for, you ask her if she remembers that gun you bought. Well honey, I sold it for $200 more than I paid for it, and the $100 bill in your hand is your half. Of course, you didnt sell anything, but theres enough guns in your critical mass that she cant tell.
My wife really likes it when I bring new guns home or when they arrive in the mail. It took me a few years of being brow beaten in order to achieve critical mass, but once I got there, its been smooth sailing ever since. You're welcome.