Translation:This watch cannot be worth one thousand zloty.
'warty' itself is Nominative here, because the construction is not much different from a sentence like "On jest duży".
Now, the real problems start: firstly, technically 'warty' is an incorrect form of the adjective 'wart' (it is very rare for the adjective to end with a consonant and it's one of the examples). But the creators of this skill only put 'warty' as a word form, so the alternative is to either keep 'warty' (which is commonly used despite being wrong) or delete all the sentences with this word at all, because it's impossible to use any other form right now.
Now... if it wasn't a number (a price, here), I would be sure that "wart/warty" should take Genitive, this is obvious. "Ona jest tego warta" = "She is worth it". And with numbers... I recently discussed it with my friend. She claimed that even with numbers it should be Genitive. I said that it sounds very weird to me and I'd use Accusative/Nominative (well, anyway, the basic form) with numbers. But I haven't found any prove of my version. So it seems that this sentence may be something that is perfectly fine in spoken language and almost no one would bat an eye... but it's possible that it has not one, but even two mistakes.
Welcome to Polish language...