Whatever type of products you sell, list building is still perhaps the most powerful way of generating profits. Build your list as the first entry point into your business.
Then create a sales funnel with your all your products.
Have one of those, or a new one created by you, as the freebie for your opt in page, as a move into your business. Then use a low cost product as the gateway into your sales funnel. You might have a group of low cost products. In which case, you rotate them in this position. So then when a subscriber purchases one of the low cost products, you move them to a higher cost products list.
Don’t have a higher cost product? Create one, because when a subscriber has bought a low cost product you increase their value to you as someone ready to pay for higher cost products rather than more low cost ones.