New 30-gallon Tank

• A new 30-gallon fish tank at a retail store can cost about $50 to about $250 as of 2010. The variation in price depends on the quality of the tank, and what accessories come with the tank. The benefit of buying a new tank is that you can usually return it if the glass or seals are cracked.
  
  

Used 30-gallon Tank

• A used 30 gallon fish tank is the cheaper option for buying a tank. If you're lucky a used tank may even be free. At the most, a used tank shouldn't be more than half the cost of a new fish tank. The drawback of buying a used tank is that it may be irreparably damaged.
  
  

Bottom Line

• Buying a used tank at a cheaper cost can be risky. You may not discover until you get it home and have it filled with water for several days that it leaks. If you are not skilled in repairing fish tanks, buying a new tank at a higher cost will be the better deal in the long run.