If you go to a store in the United States to buy a garden hose,<u> the prices will also vary</u>, but the parts will probably come attached. - NOT a noun phrase
<u>Two of the biggest factors</u> are sales taxes versus value-added taxes, and perceived value. - A noun phrase
In the United States, states need to make money to help pay <u>for the services they provide</u>. - NOT a noun phrase
There <u>will still be a wide price range</u> but all the prices – from the cheapest to the most expensive – will be much lower. - NOT a noun phrase
Explanation:
A noun phrase is a phrase acting as a subject, a direct or indirect object or an object of a preposition, that contains a noun or pronoun (also called the head), and that may contain modifiers of that head, like articles (e.g. <em>the, a/an</em>), quantifiers (e.g. <em>a lot</em>), determiners (e.g. <em>those</em>), numbers (e.g. <em>one, two...</em>) and adjectives. A phrase noun, then, does not express a complete thought on its own and does not contain verbs.
“The prices will also vary” is not a noun phrase because it has a verb “will...vary.” The phrase “the prices,” instead, is a noun phrase.
“Two of the biggest factors,” on the other hand, is a noun phrase that acts as the subject of the sentence because it has a noun, which it's <em>factors</em> (also the head), and modifiers of that head: <em>two</em> (a number), <em>of</em> (a preposition), <em>the</em> (an article) and <em>biggest</em> (an adjective).
“for the services they provide.” is not a noun phrase because it has a verb: <em>provide</em>, and does not act as a noun.
Similarly, “will still be a wide price range” is not a noun phrase because it has a verb phrase: <em>will... be</em>.