Avraham agreed to the price and not only paid him the four hundred shekalim, but paid them in a currency that would be accepted in all places. The Netziv argues (23:16) that these shekalim were extra heavy since their added value was based on their substantial weight.
Although all these explanations are interesting and add multiple levels to our understanding of the negotiations, I believe there is an additional lesson to be learned from analyzing Avraham’s actions. What would have happened had Avraham not had the foresight to bring the four hundred shekalim with him? According to all approaches, such a sum of money at that time was burdensome to transport. (It was probably not common for people to have such liquidity on hand. According to some estimations, four hundred shekalim was enough to support a person for fifty years.)
Avraham’s immediate goal was to bury his wife. His secondary and long-range goal was to demonstrate to one and all his rightful ownership (and, by extension, his offspring’s) of the land of Israel. But without the coins, Avraham would not have accomplished anything. Among the many things Avraham Avinu taught us is the need to consider logistics in order to achieve our goals. As General B.B. Somervell (Commanding General, Army Services Forces, 1942), said: “Good logistics alone can’t win a war. Bad logistics alone can lose it.”