Cheap contact lenses pose a real danger. Please beware.

Here's a press release from Illinois warning of the dangers;

Colored lenses purchased without proper examinations and fittings put thousands of Illinois customers at risk of scratches, infections and potential blindness.

...In addition to scratches from ill fitting lenses, another factor that makes this health threat so pressing is that bacteria build within the eye very rapidly. Some types of bacteria can cause permanent scarring within twenty hours of the outbreak, if left untreated. Additionally, students with irritated eyes have on occasion been misdiagnosed with pinkeye, an easily treated eye infection. However, contact lenses can cause eye ulcers which must be treated with strong antibiotic medicine. If left untreated, ulcers can cause partial or total irreversible blindness.

See the FDA page, released right after Halloween last year, with warnings about Contact Lens Safety