Here's the Grand Floridian's Wine Listit shows the price for Dom Perignon, at least. And maybe if you know the retail for some of the other brands, it will give you an idea of Disney's markup:
Champagne & Sparkling Wines
Magicale, Brachetto Piemonte DOC $49.00
Iron Horse Fairy Tale Cuvée Brut, Sonoma $62.00
Moet and Chandon, White Star Extra Dry $75.00
Veuve Clicquot, Brut N.V. $75.00
Cuveé Dom Perignon Brut $290.00
Whites
Fess Parker Riesling, Santa Barbara $37.00
Kim Crawford, Sauvignon Blanc, Marlborough $45.00
Wente Chardonnay, Livermore $39.00
Pinot Grigio, Lasorda Veneto $37.00
Sancerre, Pascal Jolivet $55.00
St. Clement Chardonnay, Napa $49.00
Cakebread Chardonnay, Napa $69.00
Blush
Kenwood White Zinfandel, CA $29.00
Red Wines
Cabernet Sauvignon
Brampton Cabernet Sauvignon, South Africa $39.00
Louis Martini Cabernet Sauvignon, Napa $47.00
Silverado Vineyards, Napa $82.00
Moon Mountain Reserve, Sonoma Organic $62.00
Merlot/Malbec
Coppola Diamond Series, CA $45.00
Clos du Bois Reserve Merlot, Sonoma $49.00
Pinot Noir
MacMurray Ranch, Sonoma $45.00
Buena Vista Pinot Noir, Carneros $49.00
Zesty Reds
Chianti Classico, Cecchi $39.00
Tintara, Shiraz, McLaren Vale $49.00
Novelty Hill Syrah, Columbia Valley $53.00
Ravenswood Zinfandel, Sonoma County $39.00