A denarius (or "penny") was what an agricultural worker typically was paid for one day's labor (Mt. 20:2). If we assume U.S. minimum wage for 10 hours, that would be $72.50 currently.
Compare this with the feeding of the 5,000 men (plus women and children), where the disciples noted that 200 pennyworth (denarii) ($14,500) was insufficient to feed the group (Mk. 6:37; Jn. 6:7).
In contrast to that, note Rev. 6:6, which sets the price of wheat at a penny per measure, or barley at a penny for 3 measures. I have been told that a measure here is enough to feed a person for a day. In other words, it would take an agricultural worker's entire wages ($72.50 per day) to feed himself on wheat; or he would be able to feed himself and two other family members on barley. This verse is obviously indicating a difficult time of some sort.