Your target market must both need your product and be able to afford it. Where not to advertise is obvious. Where you must advertise, and the medium to use, is the great trick in maximising your marketing effort and pennies. Your web site is your stall, your shop, your department store Marketing is how you get people into your store. Selling is what you do once they arrive.
Most people do.
That is a marvellous attraction of selling on the web. Your web site does the selling for you. You never have to meet a single person face to face. Your copy can make persuasive arguments that you yourself might be too embarrassed to say out loud to another human being. It is not you speaking, it is your carefully thought out words on a computer screen in Timbuktu.