"Red wine costs thirty coins."
Translation:Vinum rubrum triginta nummis constat.
I had the same thought at first. Duolingo doesn't do a good job of explaining that for a few verbs, what looks like the direct object is dative case instead of accusative. "Consto" (cost) is one of them; other are "studeo" (study), near the beginning, and "appropinquo" (approach), which shows up a bit later on.
There's a list at the bottom of
A little more context can be found at
Even more context at