Monetary responsibility of the employer in PERM

To Xiaobaito and other experts: I am thinking about going through PERM. My boss agrees to help, 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.