Monetary equivalencies are quite challenging, because we need to take into account the difference in purchasing power of gold and silver, which are frequent monetary units. I use some equivalency standards to get ballpark ideas.
Example 1: Ephron's field. Abraham paid Ephron 400 shekels of silver for the field and cave at Machpelah. What is the equivalent? Note first that we must avoid using the metal evaluation method: 1 shekel of silver was 224 grains or 0.512 ounces. As I write this, silver is selling for $18.50 per ounce. That makes a shekel worth $9.47, and the cave and field selling for $3030. Pretty preposterous, huh?
Now, let's take the labor equivalency standard. A shekel was worth 4 denarii. A day's labor paid 1 denarius. A laborer today might make $10 an hour. For a day's work, 8 hours, that's $80. Therefore, a shekel would have had $320 worth of purchasing power. The field, at 400 shekels, then sold for the equivalent of $128,000, a very possible amount.
Another method I use is the bread equivalency standard. In the eighteenth century in England, a servant, paid well, might earn 30 pounds a year. A pound this morning is going for $1.32 US. That would mean that a servant was paid only $396 a year. But wait. In, say, 1750 a loaf of bread sold for a penny. In that era, there were 240 pennies to the pound, making 7200 pennies in a 30-pound salary. An inexpensive loaf of bread today sells for $2.50, making a salary equivalent of $18,000. (And remember that servants had housing and meals as part of their compensation.)
So, what does that make a marriage settlement of 10,000 pounds a year in those days among the upper classes? 10,000 times 240 times 2.50 is 6,000,000. Six million dollars a year would put the couple on a budget, but is they shopped carefully, they could make it.
I'm sure there are other equivalences that might shed light on purchasing power for a given income in the old days. I remember in my twenties I could fill a grocery bag for $3.50. Now it takes $20 or $30.