When ordering unitards, please keep in mind that for a more authentic CATS "look" it would be best to order it white with long sleeves and a mock-turtleneck (Some characters don't use the turtleneck style. Instead, they use the crew-neck or the boat-neck style. Those character which use the crew neck are: Coricopat, Tantomile, Electra, Pouncival, Skimbleshanks, and Gus). The best material would be a nylon/lycra blend. However, there are other materials/styles that may be less-expensive.
Here are some links to where you can purchase unitards online.
ADA Discount Dancewear
Dance Choice
Discount Dancewear
NY Dancewear
Rivers Edge Dancewear