There is no definitive answer to this question as prices for building materials can vary greatly depending on a number of factors, including the type of material, the quality, where you purchase it and when you buy it. However, there are a few materials that are generally considered to be relatively inexpensive compared to others. These include wood, concrete and steel.
Wood is a popular choice for construction due to its versatility and relatively low cost. It can be used for everything from framing to flooring and is widely available. Concrete is another affordable option that is often used for foundations and walls. It is durable and easy to work with, making it a popular choice for both homebuilders and contractors. Steel is also fairly inexpensive and is commonly used for structural elements like beams and columns.