I would compare more than the final price. Look at what material is actually being specified, how it will be manufactured, who is installing it, what is excluded, the warranty and whether the company has thought about the site rather than simply priced a square metre rate.
A cheaper sign can be good value if it is the right product. It becomes expensive when it is underspecified, hard to maintain, fails early or needs to be remade. We would rather explain why we are recommending something than just tell you it is ‘premium’.