Questions & Answers about این کتاب ده دلار است.
Since the number is ده (ten), why isn't دلار (dollar) pluralized?
In Farsi, nouns that come immediately after a number always remain in their singular form. You never add a plural marker like ها after a number, so it is just ده دلار. This strict rule applies to all countable nouns.
How would you say this sentence in casual, spoken Farsi?
In spoken Farsi, the verb است (is) usually drops its first vowel and attaches to the end of the previous word. Because دلار ends in a consonant, it takes the suffix ـه (pronounced '-e'), making the spoken sentence: این کتاب ده دلاره.
Why isn't there an ezafe connecting این (this) to کتاب (book)?
Demonstrative words like این (this) and آن (that) never take an ezafe connector when pointing out a noun. They simply sit right next to the noun they modify, just like in English.
Is دلار (dollar) commonly used in everyday Farsi, or do people only use Toman?
While everyday items in Iran are priced in Toman (or officially, Rial), the US دلار is extremely common in daily conversation because of inflation and fluctuating exchange rates. However, if you are buying a local book in Tehran, it would almost certainly be priced in Toman, not dollars.