The most common way to buy bricks from LEGO stores is by filling up a PaB cup:
There are two sizes of cups and occasionally other containers that can be filled during certain promotions. The large cup is $14.99 USD and the small cup is $7.99 USD currently. This isn't advertized, but you can also buy bricks in the boxes that they are shipped to the store in. These are around $70 USD.
LEGO stores also typically allow you to build your own custom Minifigs. These include legs, torso, head, headgear, and an accessory. I believe that these are currently 3 for $9.99 USD.