That's easy, tell her you were thinking of taking up mountain biking and then show her how much a Santa Cruz Blur XC Carbon costs (it's a very nice bike and my current ride, actually one of them, you need bike quivers too!). Or compare it to the cost of a set of top notch golf clubs and annual club membership. There are a lot of sports that are far more expensive - like sailing (known as tearing up $100 bills in a salt water shower!).
I reckon a few days of bombarding her with these sorts of numbers and then quietly say (like you had a change of mind and realise how selfish taking up another sport would be) you think if you had these other boards you could surf all conditions and wouldn't need to take up another sport. And if that doesn't work and you need advice on hidden slush funds - I'm your man! I've successfully hidden $1000s of expenditure on my toys over the years. :-()

