I can't believe this hasn't been suggested yet, but:
1) Show her a few websites that sell SB
2) Tell her to pick the site and flavor(s) she likes
3) Tell her to take out her own damn credit card and buy it
5) Hope you get to at least sleep on the couch
Seriously though, I'll bet her tastes would change a bit if she had to pay for it!
[EDIT: Dammit - jonz got it in while I was typing, lol!
As an alternative, you could try bringing in some JMs - it's considerably less expensive.