As someone who has been in a vow of poverty and celibacy..woops I mean marriage for 29 years let me give you some advice...you got 3 options..
1 dont ask dont tell...never works. You will be accused of spending the money on hookers and blow.
Number 2, When you get home tell her you spent $200 at the nudie bar on lap dances and beer, then after you recover from the beating smile and say I was just joking, I spent it on a new mod....she will be all happy you did not spend it on lap dances, and then you can use her feeling guilty about smacking you around to weasel some extra stuff like batteries or some tanks.
Finally, what I found works for me buying power tools, go home and say lets go out to dinner...and it better not have a drive through window, to celebrate my new cordless drill or in this case MOD. This works great...wifee poo wants me to go to home depot all the time look honey this drill matches the other 6 you have. This does add to the cost of the new toy.