What I've been doing for Revolution preparation is this. Basically, every week when I get paid, I put some aside for the Rev, so as to get as much as I possibly can. This money is untouched and won't be touched until I can preorder Rev stuff. So far, it has been working quite well, I have saved about £150. And the total is rising.
I did a similar thing with DS, and had about £300 saved for launch, which I used for a NDS VIP Pak, 6 games and a carry case. That worked out nicely, and I hope the same for the Rev.