The price I am going to tell you is for younger Silver Dollars, the price for more mature/larger specimens varies considerably. So with you understanding that the younger one are cheaper then you should be able to find young Silver Dollars for sale for about $4-7.
The Silver Dollar is closely related to the Piranha but unlike its cousin is almost entirely a vegetarian. When young the Silver Dollar is quite timid so make sure the tank is place in an area where the outside world activities will not spook the young Silver Dollar. The roundness shape of the Silver Dollar give the it a strong presence in the fish tank. The Silver Dollar is a great addition to any tank that has other large, peaceful fish. The Silver Dollar can also be tankmates with some larger species of cichlids.
South America in rivers where vegetation is found both above and below the water.
To sex the Silver Dollar look at the anal fins. The male Silver Dollar will have a slightly larger, more colorful anal fin then the female.
The minimum tank size dimensions for housing the Silver Dollar are as follows:
48 x 18 x 18 inches (120 x 45 x 45 cm).
The temperature should be in the range of 75-82 degrees Fahrenheit (24-28 Celsius). The Silver Dollar will adapt well to most water conditions.
In the wild though the Silver Dollar is found in water that is acidic to neutral. There are no special needs that the Silver Dollar has as far as decorations in the tank goes, but it does like to have a few large hiding places under some rocks or bogwood. Like its cousin the Silver Dollar should be kept in groups of at least four or more. The Silver Dollar tends to occupy the middle and lower parts of the tank.
In the wild it feeds almost solely on vegetation and seeds, which its diet should reflect in the aquarium as well. Feed the Silver Dollars pellet foods, and for younger/smaller Silver Dollars who can not fit pellets into its mouth feed herbivorous flakes, algae wafers, lettuce, cucumber, and plant matter. Even though I named these foods off for smaller Silver Dollars you should feed all of this the the adults as well.
The Silver Dollar is very peaceful and active, but will eat almost all plant aquarium plants.
The Silver Dollar will breed in the aquarium but it needs a vary large aquarium and will also need soft water. When the male Silver Dollar is in spawning condition his colors will intensify greatly and various patterns will appear.