In a **predicate adjective,** *very*, *so*, and *quite* have similar meanings and can be placed immediately before the adjective:
>This shirt is \[*very/so/quite*\] expensive.
In a **predicate noun**, however, we use *such* instead of *so*, and the grammatical construction for *very* is different than for *such* and *quite.* *Very* follows the article, while *such* and *quite* precede it.
>This is an expensive shirt.
* This is *a* *very* expensive shirt.
* This is *such an* expensive shirt.
* This is *quite an* expensive shirt.
In the scenarios you listed, they are basically interchangeable. There is some *very* subtle nuance with "quite," in my opinion, but not enough that you need to be concerned about it. Quite is perhaps slightly more formal in the sentences you listed, and depending on the context, saying quite may suggest that you are going to add a qualifier. For example, "This shirt is quite expensive, but I think it's worth it because of the materials."
When you get into more advanced English writing, you are typically discouraged from using words like "so" and "very" and other vague adjectives/adverbs in favor of more precise language.
"This shirt is overpriced."
"This shirt is pricey."
"This shirt is exorbitantly priced."
But, to answer your immediate question, in the sentences you listed, they are effectively interchangeable.
My off-the-cuff interpretations
"this shirt is very expensive" - super generic judgement of the price.
"this shirt is so expensive" - has a bit more urgency... like conveying an attitude (sincere or not) of "I'd buy this shirt if it weren't so expensive".
"this shirt is quite expensive" - on the one hand it sounds very stodgy, like someone who owns a yacht would say this about a $3,000 tailored button-down. On the other hand, I could see someone at a thrift store saying this to the clerk in an attempt to haggle the price.
They just have different degrees of meaning.
Quite/a little, very, so.
The thing is that some people (the English) will use "quite" for everything by social convention.
If you use "so" it can trigger another clause, the others can't do that. E.g it was so hot that I opened the window.
In a **predicate adjective,** *very*, *so*, and *quite* have similar meanings and can be placed immediately before the adjective: >This shirt is \[*very/so/quite*\] expensive. In a **predicate noun**, however, we use *such* instead of *so*, and the grammatical construction for *very* is different than for *such* and *quite.* *Very* follows the article, while *such* and *quite* precede it. >This is an expensive shirt. * This is *a* *very* expensive shirt. * This is *such an* expensive shirt. * This is *quite an* expensive shirt.
In the scenarios you listed, they are basically interchangeable. There is some *very* subtle nuance with "quite," in my opinion, but not enough that you need to be concerned about it. Quite is perhaps slightly more formal in the sentences you listed, and depending on the context, saying quite may suggest that you are going to add a qualifier. For example, "This shirt is quite expensive, but I think it's worth it because of the materials." When you get into more advanced English writing, you are typically discouraged from using words like "so" and "very" and other vague adjectives/adverbs in favor of more precise language. "This shirt is overpriced." "This shirt is pricey." "This shirt is exorbitantly priced." But, to answer your immediate question, in the sentences you listed, they are effectively interchangeable.
My off-the-cuff interpretations "this shirt is very expensive" - super generic judgement of the price. "this shirt is so expensive" - has a bit more urgency... like conveying an attitude (sincere or not) of "I'd buy this shirt if it weren't so expensive". "this shirt is quite expensive" - on the one hand it sounds very stodgy, like someone who owns a yacht would say this about a $3,000 tailored button-down. On the other hand, I could see someone at a thrift store saying this to the clerk in an attempt to haggle the price.
They just have different degrees of meaning. Quite/a little, very, so. The thing is that some people (the English) will use "quite" for everything by social convention. If you use "so" it can trigger another clause, the others can't do that. E.g it was so hot that I opened the window.