Low-grade chassis are iron plate (steel plate), some high-grade is also a steel plate, but the workmanship is very different, accessories are also different.
Aluminum chassis belongs to the high-grade, generally good workmanship, the price is also higher.
Acrylic is mainly used in the side perspective, high-end low-end are used, but not the main material.
Plastic is also generally used as chassis parts, will not be used as the main material.
But chassis generally have more than one material. Overall the aluminum chassis is a little better, but will also use steel, plastic, acrylic materials. The thickness of the materials used, the workmanship, the design, and the configuration are the comprehensive reflection of the value of the chassis.