"Cheap grace" is what we create when we sin anyway figuring that God is always going to be willing to forgive us. Buying into it gives a way out of doing the hard work of penance. When we go back to that 51st Psalm of David, we hear the agony of a repentant man who faced his sin and was horrified at what he had done to himself and what he had done against God. He knew his only hope was the love and mercy of God. "Have mercy on me, O God, according to Your steadfast love; according to Your abundant mercy, blot out my transgressions." When we are truly penitent, we, too, know that we are undone, without hope unless God steps in to change the direction of the consequences of our sin.
If Lent is truly a season of preparing the heart to be in the presence of God, then this work to which the Lenten invitation beckons us is something which should take precedence over all the other work of our life. The thing David feared the most was being cast away from the presence of God and having to live without an awareness of the Holy Spirit in his heart. With such serious consequences out there awaiting us because of our sin, the work of penitence can never be seen as too costly.