Petit Chablis - This can be the suspect area category. The fruit comes from the soils which lack the stong limstone content elsewhere.
Chablis (In your Case) - This comes from vineyard locations that enable the wine to extract the purest flavours from the soils. Perhaps Burgundy's most important appellation in terms of quality.
Premier Crus - Now you are shopping by vineyard name. Around 40 vineyards have this status and it is all to do with the limestone makeup of the soil and the vineyard elevation.
Grand Cru Chablis - This accounts for less than 3% of Chablis production. The vineyards are located in a single band just above the town of Chablis. There are only seven Grand Crus which have a global reputation, so this of course effects the price