Adam Clarke on Exodus 8:28

I will let you go only ye shall not go very far away - Pharaoh relented because the hand of God was heavy upon him; but he was not willing to give up his gain. The Israelites were very profitable to him; they were slaves of the state, and their hard labor was very productive: hence he professed a willingness, first to tolerate their religion in the land, (Exo 8:25); or to permit them to go into the wilderness, so that they went not far away, and would soon return. How ready is foolish man, when the hand of God presses him sore, to compound with his Maker! He will consent to give up some sins, provided God will permit him to keep others.

Entreat for me - Exactly similar to the case of Simon Magus, who, like Pharaoh, fearing the Divine judgments, begged an interest in the prayers of Peter, Act 8:24.