Final answer:
A survey is the quickest and least expensive method for studying the development of a large group of people, as it can gather a lot of data rapidly and cost-effectively.
Step-by-step explanation:
The quickest and least expensive way to study the development of a large group of people is through a survey. Surveys allow researchers to collect data from subjects who respond to a series of questions about behaviors and opinions, often in the form of a questionnaire or an interview. This method provides large amounts of information in a relatively short amount of time and can be administered to many individuals simultaneously. While the data collected may not be as deep as that obtained from methods like in-depth interviews or case studies, the efficiency and cost-effectiveness of surveys make them a popular choice for researching large populations.