There is generally priced based on how much capacity it generates (measured in Watts), the physical size of each panel, the durability or warranty period offered, the quality of materials used in it as well as the types of certifications that the panels have.
The price may also vary depending on how many panels are being purchased as part of the package – the general rule showing the price decreasing with an increase in a number of panels in the package. However, it is to be kept in mind that price is never the primary factor to take into account when purchasing a solar panel. The panel will have to fit the purpose perfectly in order to give its maximum performance.