There are multiple ways to price things.
1 way to help on some projects you can use http://www.thesignexpert.com/TheSignExpert.com/Sign_Business_Free_RTA_Vinyl_Price_Calculator.html for a base line
another a lot seem to use is length +width / 2.
For example I was recently having a hard time pricing a bigger then normal (for me) job. I decided to do the quotes both those ways then since they were a lot different, I went with the medium of the 2. But regions are different and since I cant see where your from, I dont know what will work for you.