Adam Clarke on Genesis 23:15

The land is worth four hundred shekels of silver - Though the words is worth are not in the text, yet they are necessarily expressed here to adapt the Hebrew to the idiom of our tongue. A shekel, according to the general opinion, was equal to two shillings and sixpence; but according to Dr. Prideaux, whose estimate I shall follow, three shillings English, four hundred of which are equal to sixty pounds sterling; but it is evident that a certain weight is intended, and not a coin, for in Gen 23:16 it is said, And Abraham weighed וישקל vaiyishkol, the silver, and hence it appears that this weight itself passed afterwards as a current coin, for the word שקל is not only used to express a coin or piece of silver, but also to weigh; See note on Gen 20:16.