Sustainable tourism management is becoming an increasingly important factor in the image of tourist destinations. Therefore, it is appropriate to consider the possibility of charging a premium price on certain tourism products or services in exchange for making them more sustainable. Generally, eco-friendly management of cultural heritage sites, and particularly World Heritage sites, along with protected natural areas, is essential for the image enhancement of tourist destinations. In line with these considerations, this paper aims to quantify the willingness to pay (WTP) an extra amount in order for certain tourism products and services to become more sustainable in a World Heritage city such as Caceres, Spain. By using the contingent valuation method, the average price increase that tourists visiting the city would be willing to pay for a double room in a hotel, a restaurant, entrance to a museum, or a taxi ride, all of which would become more sustainable services, has been estimated. In addition to the aggregate analysis, diverse average-comparison statistical techniques have been used in order to determine the possible influence of sociodemographic factors on the WTP for more sustainable products and services. Specifically, factors including the effect resulting from a tourist’s place of origin, gender, the year when the survey was conducted (through t-tests), and the effect of age and educational levels (through ANOVA tests) on the WTP for sustainability, have been analyzed. When considering all of the sociodemographic factors involved, notable statistical differences have been found. This implies that when a hypothetical increase in tourism prices for the purpose of financing public or private sustainability actions is considered, different segments of the tourism market should be taken into account, since it would not be appropriate to apply the same policy of price increases to all tourists equally.