Translation:Eight hundred and eighteen crowns is left.
Grammatically the use of the singular verb is correct. https://owl.english.purdue.edu/owl/resource/599/01/ See #7
My own instinct is to pluralize it, and I think colloquially a lot of people would.
This came up in the past. Since a word for word translation is often impossible, I feel that imposing the Czech use of singular verbs when dealing with multiple objects into English is odd at best. At the reference suggested above I find: There were one hundred and thirty-five pieces in the puzzle, which is correct in English.
We would never force Czech grammar in English, that would just be nonsense.
It is, because you are not talking about plural actual individual crowns (as in your puzzle pieces) but their singular amount value. The meaning is always more important than keeping strictly to one form. That's a mere formality. In English every rule has exceptions after all.