Learn French: Ce livre coûte dix dollars. - This book costs ten dollars.

You would use the suffix -aine with the number dix to make dizaine. The sentence becomes Ce livre coûte une dizaine de dollars. Notice that you must add une before dizaine and de before the noun dollars.

Is the 'x' in dix pronounced in this sentence?

No, the 'x' is silent here. When dix is followed by a word starting with a consonant, like dollars, it is pronounced like 'di'. It only sounds like 'dis' when used alone or at the end of a sentence, and makes a 'z' sound before a vowel.

Why do we use Ce instead of Cet or Ceci for 'This'?

Ce is the masculine singular adjective for 'this' or 'that', used right before a noun starting with a consonant like livre. You would only use cet if the masculine noun started with a vowel or a mute h. Ceci is a pronoun meaning 'this thing' and is used on its own, not attached to a noun.