This budget thing will never work. Firstly, what's stopping for example, Force India and Toro Rosso from compliance with the cap, complete loads of testing and feed some of the results back to Mercedes and Ferrari, who will eventually pass it on to the Mclaren and Ferrari works team?
But there's no need to be so underhanded, how do you split marketing and hospitality costs. For example, the huge "brand centres" that were in the pre-show apparently cost over £40m a year to run, all hospitality, or at least that's what they'd say, but what's stopping them fudging exactly how the suite is used, and how design staff back at the HQs are used. Toyota could easily reassign internal engineers and just no say anything.
I don't oppose the principal of a bidget cap, but I think it's too much, too soon. I also don't like the idea of a voluntary budget cap. I'd be much happier if it was an all or nothing scheme.