It really depends on the sort of thing you want to do. How much you need or want to earn and so on. You will be competing with goodness knows how many other online stores so need to consider what you plan to market/sell, how you will supply etc. Do you have a business plan drawn up? Same principals apply to online stores as in the high street.
I run websites but they are not there for the sole purpose of selling things, more to be informative etc. I earn money from them because o Google ads, Amazon affiliate programme and tee shirt sales.
You can spend a fortune paying someone to design a website for you, a sales system and so on but its really easy to make your own, set up hosting and a domain and get it going. No need to pay anyone.