Blanc de blanc....
The SF Chronicle had some good articles last week on this topic. Here are some links, and an interesting note from them about one of their tastings that might fall in your budget.
"The luxe 1999 Louis Roederer Cristal ($188) was as subtle as it was sublime, but not so different from the 1999 Roederer Estate L'Ermitage Anderson Valley ($49) that the latter wouldn't make an excellent alternative for those buying bling on a budget. "
"no varietal indication is it going to be just a crap shoot?"
Not quite. Watch the Forbes slide show (in link below), lots of no varietals amoung the top dollar babies.
As far as my favorite Krug goes, most of their products are blends:
"No real recipe, every year they have to make the blend with 25 to 40 plots of Pinot Noir, Chardonnay and Pinot Meunier. The reserve wines part will be 30 to 50%, from 6 to 8 millesimes... This selection through multiple tastings is Art : The Grande Cuvée 2005 is made with 82 different wines when you count the varieties, the plots, the villages and reserve wines..."
There are three permitted varieties in Champagne*. They are Pinot Noir, Pinot Meunier and Chardonnay, the latter being the only white grape variety. Thus, IF you see the designation "Blanc de Blancs" on a bottle of [true, real, from the region] Champagne, then you will know it's 100 percent Chardonnay.
French sparkling wines from anywhere OUTSIDE the Champagne district, let alone those produced outside France, which are labeled "Blanc de Blancs" may contain ANYTHING** -- read the fine print (and you still may not know).
* There are some other grapes permitted under a "grandfather clause," but the total acreage is insignificant.
** anything, that is, as long as it is permitted under the regulations governing the production of that wine in that place.