Whipped cream is a bad way to go - You'll pay a couple bucks for not much nitrous. A good price on chargers is $0.50 or so each. $1 is the most you should pay. Buy them at a store (some grocery stores, speciality food stores, porn shops and head shops carry them) or google for an online vendor. The cracker is best obtained at a head shop; the cannisters can be bought online or at many stores that sell the chargers.
