Clownfish are the cheapest aquarium fish variety in this list with an average price tag of $40 for the most expensive species i.e. the black & white percula. These type of aquarium fish is popular because of a number of reasons the most notable being; they are easy to maintain. Clownfish are the best for novice aquarists because of a number of reasons i.e. they are not delicate, needy or susceptible to diseases. They also breed freely and easily. The cheapest Clownfish costs under $10.