How can something cost x coins? Surely it should be x denarii or y sestercii.
If giving an English translation is the problem, you can translate sestercii as "shillings" and denarii as "pence".
What declension is nummis? In the accusative it would be nummos, so would nummis be dative?
It's the ablative plural from what I understand.
Richlogos explains a little more in this discussion: https://forum.duolingo.com/comment/33979400
Is it just me, or in many audios starting with the letter "P" this letter sounds like an "H"?