Дешево is an adverb. It does not connect to any noun. Using in a sentence: "Це дуже дешево" (This is very cheap), "Ми подорожуємо дешево" (We travel cheap)
Дешевий (m), дешева (f) and дешеве (n) are adjectives. They are connected to nouns. Дешевий будинок (cheap house), дешева машина (cheap car), дешеве молоко (cheap milk)
Therefore, "Дуже дешевий" is not really a full sentence as it lacks a noun. Can be a short response in a dialogue:
Цей будинок дешевий?
Should it or should it not be accepted as a translation of "Very cheap" is a separate question that boils down to whether "Дуже дешевий" can be considered a sentence...
Дякую Sagitta! Я розумію зараз. I know you didn't want the lingot last time so here's another coming your way.