warrenr offers good advice on figuring out the wine pricing structure of various restaurants: don’t use benchmark wine prices.
To explain: some folks check the prices of three or four very well-known wines and champagnes, to figure out the house’s markup. The problem is that sommeliers anticipate this, and will frequently mark down the price of, say, Veuve Clicquot, just to fool consumers.
And some have variable pricing structures: a lot of places mark up non-vintage champagnes heavily, while offering bargains on prestige cuvees.
The moral: the only way to figure out the markup is the hard way–knowing the retail prices of lots of individual wines.
Board Links: ISO Price Benchmark Wines