Printful product prices include:
The product itself
Standard product customization
Mockup previews and downloadables (with a connected store)
Note that in some cases, there are extra costs:
Embroidery digitization fee (one-time fee for each design you digitize, added to the price of the first product you buy/sell with this design)
Extra customization (sleeve prints, additional embroidery, or large prints)
Fee for using Premium Images in your design
Product label fee