Adam Clarke on Leviticus 25:50

The price of his sale shall be, etc. - This was a very equitable law, both for the sojourner to whom the man was sold, and to the Israelite who had been thus sold. The Israelite might redeem himself, or one of his kindred might redeem him; but this must not be done to the prejudice of his master, the sojourner. They were therefore to reckon the years he must have served from that time till the jubilee; and then, taking the current wages of a servant per year at that time, multiply the remaining years by that sum, and the aggregate was the sum to be given to his master for his redemption. The Jews hold that the kindred of such a person were bound, if in their power, to redeem him, lest he should be swallowed up among the heathen; and we find, from Neh 5:8, that this was done by the Jews on their return from the Babylonish captivity: We, after our ability, have redeemed our brethren the Jews, who were sold unto the heathen.