A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
gen 23:1AGE AND DEATH OF SARAH. (Gen 23:1-2)
Sarah was an hundred and seven and twenty years old, &c.--Sarah is the only woman in Scripture whose age, death, and burial are mentioned, probably to do honor to the venerable mother of the Hebrew people.
gen 23:2Abraham came to mourn for Sarah, &c.--He came from his own tent to take his station at the door of Sarah's. The "mourning" describes his conformity to the customary usage of sitting on the ground for a time; while the "weeping" indicates the natural outburst of his sorrow.
gen 23:3PURCHASE OF A BURYING-PLACE. (Gen. 23:3-20)
Abraham stood up, &c.--Eastern people are always provided with family burying-places; but Abraham's life of faith--his pilgrim state--had prevented him acquiring even so small a possession (Act 7:5).
spake unto the sons of Heth--He bespoke their kind offices to aid him in obtaining possession of a cave that belonged to Ephron--a wealthy neighbor.
gen 23:9Machpelah--the "double cave."
gen 23:10Ephron dwelt--literally, was "sitting" among the children of Heth in the gate of the city where all business was transacted. But, though a chief man among them, he was probably unknown to Abraham.
gen 23:11Ephron answered, Nay, my lord, &c.--Here is a great show of generosity, but it was only a show; for while Abraham wanted only the cave, he joins "the field and the cave"; and though he offered them both as free gifts, he, of course, expected some costly presents in return, without which, he would not have been satisfied. The patriarch, knowing this, wished to make a purchase and asked the terms.
gen 23:15the land is worth four hundred shekels, &c.--as if Ephron had said, "Since you wish to know the value of the property, it is so and so; but that is a trifle, which you may pay or not as it suits you." They spoke in the common forms of Arab civility, and this indifference was mere affectation.
gen 23:16Abraham weighed . . . the silver--The money, amounting to Â£50 was paid in presence of the assembled witnesses; and it was weighed. The practice of weighing money, which is often in lumps or rings, each stamped with their weight, is still common in many parts of the East; and every merchant at the gates or the bazaar has his scales at his girdle.
gen 23:19Abraham buried Sarah--Thus he got possession of Machpelah and deposited the remains of his lamented partner in a family vault which was the only spot of ground he owned.