Thanks Edinburghzombie. Yeah, when I got those novelty contacts, I had to go for an eye exam and order them through the eye doctor (since contact lenses are considered a medical device and require a prescription).
When I got them, I asked how long they would be good for. I was basically told... however long they last. They don't "go bad" so as long as I keep them in the solution, they won't dry out and I can keep on using them.
If they ever rip or feel weird in my eyes, I'd retire them. But until then, I'm doing my best to get my money's worth!