FB Ads any spending references

ok, the truth is I always avoid paid ads at all costs, and I used only organic traffic to my stores, free marketplaces, and interesting FB posts, Offers, adding collections etc, but I never boost anything with Ads, as for what I read is really an unknown territory, so let's say you target just one South Florida city, is it better to advertise a collection, or a single product, so they click and check your site? By the example above I meant, to go for the niche, and what will be the minimum recommended ad spend?, to get at least enough data, and that has some ROI, are we talking about a total spend, about $50, $100, $500, per the whole campaign, as I said I have 0 experience, and I don't feel comfortable burnin' money, as I have a very limited budget, so the A/B tests, experiments, whatever, need to be optimal, I am selling on marketplaces, but I want to boost my online stores, one is a perfume shop, the other is electronics, and is all in my VPS, so I am running Zen Cart on one and woocommerce on the other, as ecommerce platforms, paid advertising it's a last resort. I tried monetization, Amazon affiliate programs, AdSense, all kinds of different channels, and the results were really disappointing, Amazon eat up 30% in taxes and I got a mere $77.87 after months of optimizing and posting, not any interesting income from there, I do have another domain and an ecommerce store also using woocommerce but for tools and flooring, but that one is merely empty, in the past I really had excellent results with Google Shopping, but that was in 2006-2009, can't remember exactly when it ended but it was before Google Shopping turned into paid, but due to the GTINs, most of my products gets instantly disapproved, due to the lack of UPC. So my question is is there a time frame you normally use when doing these campaigns that works for you?