I keep seeing pearls online for �50, �100 are they real ??? They cant be???... but it doesnt say man made?

I want to by some nice pearl jewelery. I went on ebay and people were selling them for �5 �10 just so cheap but in their description they were say real and when I sent a message to these people they still told me they were real. Then when I start looking all over online I was seeing such cheap prices... Are these pearls real but just a cheaper quality? I always thought pearls were really expensive...???