ppc question for Amazon stores

Hi, I have 10 amazon stores and I am looking to do some ppc advertising. The sites are niches and have things ranging from $40 to $700. My goal is to at least make 40 or 50 a month through amazon per site. But this is my first time doing ppc and I am not sure how much to put in adwords for my per day budget. I cant put a lot if I might only be able to make $50 a month. Just curious what a average budget per day and bid is for a niche amazon store if anyone has done them before. Thanks again

our budget $100 per day