To Xiaobaito and other experts: How much my boss has to pay..

My boss agrees to help me with the PERM (EB2), but he asked how much money he has to pay during the process that is required by the law. I know some lawyers they ask for the money of the whole package of I-140, but that is thousands of dollars, and I wonder only a portion of it has to be paid by the employer and I can pay the rest. Am I right? Please advise. Thanks ahead.