Costs?

I am going to start my first drop shipping site. I have a very specific niche in mind, I am going to pay for instagram promos, maybe fb ads as part of the marketing.

What is the optimal method of running a drop shipping store considering costs and performace, I have seen various ways in which people are able to run these stores, some cheaper than others. Any advice? I want to initially keep costs reasonably low to begin with as I doubt I'll make instant sales.