You can buy fashionable shoes at a good price.
(Is 'at a good price' an adjective phrase modifying 'shoes'? Or is 'at a good price' an adverbial phrase modifying 'buy'?)
Question 2: Does 'at a good price' mean 'at an expensive price' or 'at a reasonable price' or 'at a low price'?
The phrase "at a good price" is an adverbial phrase modifying "buy."
It means at a reasonable price.
In order to determine whether "at a good price" is an adjective phrase modifying "shoes" or an adverbial phrase modifying "buy," you can analyze the structure and meaning of the sentence.
When you say, "You can buy fashionable shoes at a good price," the phrase "at a good price" provides additional information about the act of "buying." In this case, it answers the question "Under what condition or at what cost can you buy fashionable shoes?". Therefore, "at a good price" acts as an adverbial phrase modifying the verb "buy." It tells us more about how the action of "buying" occurs.
To sum up, "at a good price" is an adverbial phrase modifying the verb "buy." It provides information about the condition under which the action takes place.