The Lord called simple people full of faith to carry out the preaching of the gospel so that it would be clear that it was not the brilliance of these men that was responsible for the success of the preaching of the Gospel.
1 Corinthians 1:23-31 but we preach Christ crucified, to the Jews a stumbling block and to the Greeks foolishness, 24 but to those who are called, both Jews and Greeks, Christ the power of God and the wisdom of God. 25 Because the foolishness of God is wiser than men, and the weakness of God is stronger than men. 26 For you see your calling, brethren, that not many wise according to the flesh, not many mighty, not many noble, are called. 27 But God has chosen the foolish things of the world to put to shame the wise, and God has chosen the weak things of the world to put to shame the things which are mighty; 28 and the base things of the world and the things which are despised God has chosen, and the things which are not, to bring to nothing the things that are, 29 that no flesh should glory in His presence. 30 But of Him you are in Christ Jesus, who became for us wisdom from God––and righteousness and sanctification and redemption 31 that, as it is written, "He who glories, let him glory in the LORD."
What is meant by the cost of discipleship is that we must be prepared to sacrifice all for the sake of the Gospel. For some of those to whom the Lord spoke, this would be a literal sacrificing of their lives because of persecution.
The apostle Paul gives us a good insight into the total commitment required to follow Christ:
Romans 12:1,2 I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. 2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
I hope you have found this helpful.