"How much do the lörtsy cost?"
Translation:Paljonko lörtsyt maksavat?
If it was singular, the English sentence would be How much DOES the lörtsy cost?. However, I think lörtsy could be pluralized in English to lörtsys. Otherwise it can be confusing. In fact, I also wrote Paljonko lörtsy maksaa? for the first time because I just looked at the noun, not at do.