Want to adopt my best friend's baby..help

:confused: Hi everyone...my best friend is pregnant and wants me and my fiancee to adopt him or her. My question is, does anyone know about how this would work? Like, would it be a bit cheaper in price since it's basically "direct placement"...we don't need anyone to find us a baby. Also, can the paperwork for the adoption all be signed and legalized before she gives birth, or do we all have to wait until the baby is born. If we have to wait until the birth, does she have a certain amount of time after the papers are signed to change her mind and keep the baby? Sorry to have so many questions...I'm very new at adoption. Any help would be very much appreciated