Sarah died at age 127 (Gen 23:1).  Isaac would have been in his 30's.  Abraham had to buy land from the Hittites to bury her.   Abraham called himself "an alien and a stranger among you" (Gen 23:4).  Despite all the flowing words of Oriental courtesy between himself and Ephron, he was quoted an exorbitant price, 400 pieces of silver, for the cave of Machpelah.   At the end of the transaction, Abraham was no longer an alien in Canaan, but a landowner.  The  purchase of land can be viewed as an expression of faith in God's promise of a homeland (NIV Study, p.40).  
       
For a later example of a similar sign of hope, see Jeremiah's purchase of his cousin's field in the village of Anathoth prior to the Babylonian captivity (Jer 32:9).

          

Abraham remarried a woman named Ketura (Gen 25:1).  The ethnicity of Keturah is not known, but she could well have been a Canaanite.  He had 6 sons by her!  One of these was the founder of the Midianite nation.  All of these later offspring he sent away from Isaac and from Canaan (Gen 25:6).  As God had set Abraham apart from his two brothers, so Abraham exalted Isaac above Ishmael and all his other sons.  None of these other sons shared in  the blessing of the covenant.