Money is a form of currency that is used to pay for an item or service. Mr. Krabs is known to be obsessed with it as seen in many episodes throughout the series, beginning with the pilot episode "Help Wanted."
Known units and amounts
The money in SpongeBob SquarePants is the U.S. currency, loosely supported by the fact that Bikini Bottom is part of the United States. Known amounts include the penny, nickel, dime, quarter, one-dollar, five-dollar, and twenty-dollar bill. The largest known unit is a one hundred million dollar bill.
The city of Atlantis has its currency, but it appears to be gold, gems, and other seemingly golden objects. It is also said that the Atlanteans were not obsessed with wealth, as opposed to one of their visitors, Mr. Krabs. Nothing is known about the worth of the currency.
As seen in the episode "Mr. Krabs Takes a Vacation," all of the money in Bikini Bottom is made at the Bikini Bottom Mint. There, the money goes through different processes to be made. There is even a step where old money is burned up and created into newer money.
Dollar bills are made from "very special sheets of paper" (made with 75% cotton and 25% linen) that are specially prepared to be the standard for money. Coins are made from sheets of metal pressed into coins. Money is also recycled by shredding money and then processing them into brand new cash.
In the episode "Mr. Krabs Takes a Vacation," Mr. Krabs and SpongeBob receive their own money with their faces on it.
In many episodes, Bikini Bottom's population is seen to be quite small. In the episode "Clams," Mr. Krabs earns his one-millionth dollar, indicating millions of bills have been spent in Bikini Bottom, despite its small population. Mr. Krabs is also seen to have a large quantity of money in his vault at the Krusty Krab in various episodes.
Sometimes, money (mostly coins) has the ability of speech and moving the face of the figure just as a gag. Examples include: