Nitrous Oxide (No2), or laughing gas, is nothing like novocaine. It is inhaled through a mask to make you relaxed so it is easier to give you anesthesia, typically for oral surgery or if it is an operation without general anesthesia. Novocaine is a local anesthetic to deaden the feeling in a specific area so as not to feel pain. Nitrous is very short lived, if you only had the gas it would wear off within minutes of the mask being removed, and would still feel any work being done anyway (it is not an anesthetic). If you are asking about price... I am guessing nitrous is probably cheaper, but basically a mute point since it won't work.
