As a rule fair trade products do not cost more than non-fair trade products though some major retailers will charge a premium for this type of product because of the perceived consumer value, this is often referred to as greenwashing. 
In General small independent fair trade merchants will not charge this type of premium on the products that they sell. Fair traders tend to work directly with the producsers and artisans, this often cuts out anywhere from 3 to 10 middlemen that each add costs to the product that goes through a more normal supply chain. This allows the fair trade merchant to pay more to the supplier without adding cost to the consumer.