Adam Clarke on Jeremiah 32:9

Weighed him the money - It does not appear that there was any coined or stamped money among the Jews before the captivity; the Scripture, therefore, never speaks of counting money, but of weighing it.

Seventeen shekels of silver - The shekel at this time must have been a nominal coin; it was a thing of a certain weight, or a certain worth. Seventeen shekels was the weight of the silver paid: but it might have been in one ingot, or piece. The shekel has been valued at from two shillings and threepence to two shillings and sixpence, and even at three shillings; taking the purchase-money at a medium of the value of the shekel, it would amount only to about two pounds two shillings and sixpence. But as estates bore value only in proportion to the number of years before the jubilee, and the field in question was then in the hands of the Chaldeans, and this cousin of Jeremiah was not likely to come back to enjoy it after seventy years, (nor could he then have it, as a jubilee would intervene and restore it to the original family), and money must now be very scarce and high in its value, the seventeen shekels might have been a sufficient sum for a field in those circumstances, and one probably not large in its dimensions.