A glass of Chalk Hill Imagine Chardonnay is around $11 from memory. That compares with around $7 for a glass of Rosemount Estate (which should give you a steer on the quality, assuming you're familiar with it). A glass of Mumm champagne from the cart in France will set you back around $14.
As the wines on the shops are from that country and therefore imported they can get very high! I am guessing a good bottle of wine would be in the region of $50, champagne could well be alot more.
I you are at the AKL then check the resort shop, they have bottles there(no idea what) still probably twice price of a liquor store but should be cheaper than Epcot.