Let me share with you a conversation my cousin and his wife had about the cost of salvation.
My cousin brought up how amazing it is that God offers us salvation absolutely free; surprisingly enough his wife said that God does not. Then came a back and forth spousal "He does" and "He does not" and finally my cousin asked "what do you mean?". The response was "Salvation costs us everything". What makes this conversation so profound is that both my cousin and his wife are absolutely correct. Let me explain:
We (mankind) are dead in our sins, awaiting a day when God will judge us according to His law (the 10 Commandments) - the verdict can only be guilty (because we have all broke God's law; from lying and stealing and lusting, all the way down the list), the sentence can only be hell (the just and righteous sentence from a just and righteous God). We are hopeless :(
But God made a provision for us that would allow us a way to be forgiven and made right and at peace with Him. He put on flesh and blood becoming man (Jesus Christ) lived sinless, and then died for us - because of our sin, in spite of our sin, and to cover our sin (and then He rose again the third day just as the prophets recorded in the Old Testament). What happened 2000 years ago was that even though we broke God's law; Jesus paid our fine - WITH HIS BLOOD. And if we repent (turn from sin to Jesus) and put our faith in Him (entrust ourselves to Him, as our only hope) we will be granted eternal life. This is the Gospel truth, the message of salvation. But I haven't yet explained how it is free to us and at the same time costs us everything - so here goes.
What makes salvation free? It is free because we can't purchase it, we can't earn it, and it is offered to anyone and everyone. To clarify what is meant by our inability to purchase or earn salvation, there is nothing from our life that we can offer God that says we deserve salvation. Our life is filled with disobedience to God and our "good deeds" cannot begin to be payment for the life of the Creator of the universe, especially because they cannot negate our wickedness (bad deeds). Salvation is free because in utter deserved condemnation, Jesus offers salvation to anyone and everyone regardless of the fact none of us deserve it, or can earn it; regardless of the fact that all of us have earned (the wages of sin) and deserve hell. Salvation is free because Jesus says it's not what you have done, It's what I (Jesus) have done. - so what do we do about that? This is where we can see salvation costs us everything.
What makes salvation costs everything? It is the repentance and faith that we must put in Christ to be saved - which when we do, we are surrendering our life to Christ. We are turning over the ownership of ourselves to Him - and there cannot be anything we refuse to let go of when we make this choice. And to be a little more clear, it was brought up that we cannot purchase salvation; more than dying as payment for sin, Jesus was purchasing us - we cannot accept His payment for our sins, if we are not simultaneously accepting his salvation as payment for our lives. We cannot accept Him as Savior if we are not accepting Him as Lord.
So the choice is clear. Jesus gave His life (freely) to offer you life (which you don't deserve) if you'll surrender your life.