Coin Value

When I read the Bible text, and then going to commentaries, I see that they are so much off with money value conversion to our days. Some are not realistic, using just a common sense. Using the Bible passage:

"Are not two sparrows sold for a copper coin?" Mt 10:29.

Some commentaries say that in our days copper coin is a fraction of a penny. Realistically, who would sell 2 or 5 birds for less than penny. Who would waste their time to bring birds, sell, and not earning anything? It is just not just realistic. 

I began to use Denarius is a standard for money conversion since I know approx. minimum day salary. Based on that, I converted coins values. Based on my conversion, 2 small birds would cost around $5. Which look more realistic to me

Is my conversion look realistic enough? What would be good resources for coin values?

I have the most problems with smaller coins:

• ἀσσάριον (assarion) (Pennies - Copper Coin)
• κοδράντης (kodrantēs) (penny)
• λεπτόν, (lepton, mite) (penny)

Here is my conversion list, your input, suggestion would be appreciated:

Denarius =  δημάριον (dēnarion, denarius) $.20  day’s wage of minimum salary = $100

Drachma - Greek Coin = δραχμή (drachmē, drachma) $.16 day’s wage of minimum salary =$80

Shekel (4 drachmas) = $350 "silver coins"

Small Coins:

• ἀσσάριον (assarion)c. $.01  - 1/16 of a denarius = $5-$6 (Pennies - Copper Coin)
• κοδράντης (kodrantēs) 1/4 of $.01 - $1 (penny)
• λεπτόν, (lepton, mite) 1/8 of $.01 = $.50 (penny)

Lewis A. Foster, “The Metrology of the New Testament,” in The Expositor’s Bible Commentary: Introductory Articles, ed. Frank E. Gaebelein, vol. 1 (Grand Rapids, MI: Zondervan Publishing House, 1979), 613.

Talent: Roman-Attic talent, which comprised 6000 denarii or drachms = $500,000-$600,000

Mina: is the sixtieth part of the talent, 100 denarii = $8,000

Archibald R. S. Kennedy, “MONEY,” ed. James Hastings et al., A Dictionary of the Bible: Dealing with Its Language, Literature, and Contents Including the Biblical Theology (New York; Edinburgh: Charles Scribner’s Sons; T. & T. Clark, 1911–1912), 428.