Translation:The price of the kitten is thirty euros.
Why is there an accusative on euros in this case? I understand using it for length. But wouldn't there be a difference between "the street is one kilometer long" and "the length of the road is one kilometer"? Which would be "la strato estas unu kilometron longa" and "la longeco de la strato estas unu kilometro" respectively. Wouldn't the same thing apply to euros?
Yeah.... That's an interesting question... I've found something in PMEG that may help a bit on the topic "Akuzativo por Mezuro": http://bertilow.com/pmeg/gramatiko/rolmontriloj/n/mezuro.html It says: "Diversaj mezuroj - Aliaj mezuroj funkcias tute same kiel tempaj mezuroj. Povas esti mezuro de spaca longeco, alteco, larĝeco, distanco, profundo, pezo, KOSTO k.t.p. " In fact, I think the "n" in "eurojn" is to say "tridek da eŭroj" : http://bertilow.com/pmeg/gramatiko/rolmontriloj/rolvortetoj/da/bazaj_reguloj.html
In the frase "La longo de tiu ĉi tapiŝo estu dudek ok ulnoj" As you can see, the direct object is not governed by the accusative case because the sentence also have the verb esti, which is a copulative verb and verb and these are not followed by the accusative case.
NOTE: copulative verbs are those who talk about the state of the subject, while descriptive verbs are those who descripve them, so "to seem", "to be", "becase". "stay". "be called", "keep" an others ALWAYS get this ending in Esperanto (when have this function obviously)