Cost very simply refers to literally the cost of learning a new language such as time and money. Cost must also be seen in relation to benefit. This is very important in understanding agent related complexity.

For example, in Singapore, the cost of learning Italian may be high as it will require a lot of time and energy. The benefit is also low to the common man as they are unlikely to get much opportunity to actually speak Italian beyond the classroom. However, for a Singaporean student going on exchange to Italy or migrating there, the cost benefit is much higher and from their point of view the cost will seem lower. To the first person the value of time will be seen as high due to the low rewards but to the second, the value of time will be seen as less expensive. Hence cost as well is a very subjective verb and cost can range depending on what the person in question determines as important. If the person places more importance on time than money, and the language is easy to learn though it costs more, it will be seen as less complex to them. This again reflects the problematic subjective nature of the agent-related model.