I am interested in adding a suppressor to my Saiga AK-74 (5.45X39). This will be the first time I have done this and I'm not sure what I will need. I am sure I will need to purchase a new barrel as well as the can itself but I would like some input as to what else I will need. I will be taking it to a gunsmith and just want to be sure I'm not getting ripped off. Any advice would be huge. I'm retiring after 20 years in the Army and this is my retirement gift to myself.

Congrats.  I do not know why you would need a new barrel.  Talk to ADCO and tell them what you want, and they will make it happen with your barrel and the thread pitch you choose. Local gunsmiths are okay, but the threads need to be done concentric.  ADCO does it for a living and specializes.