The type of coin is not stated in the text, but the most common silver coin was the silver denarius, which was worth about a day's pay.
So 30 silver denarius would be about a month's pay.
The weight of the silver was about 3.8 grams, according to this source:
30 x 3.8 = 114 grams
price of pure silver coins today, is between $15 and $20 per ounce
114 grams is about 4 ounces
so the silver in the 30 denarii is worth $60 to $80 U.S. dollars, about a day's pay for a relatively low paying job.