"The fruit here is cheap."
Why do I need 的? For me it works fine without it... (but of course I am here to learn ;) )
You are connecting a place, you could say 在这里水果很便宜 水果在这里很便宜 Using 在 to mark the place and put it before the predicate or You can qualify the noun 水果, as if 这里 would be an adjective, in this case, the particle for that is 的 and you can regard 这里的水果 as a single thing: fruits with the quality or property of being "here"!
Why do the comments remove the "new lines", is screws up all the text! Does this happens only in the app?
Should be accepted in my mind. What is wrong with it? Normal Chinese sentence structure is Sub+Place+Verb+Obj. Shouldn't 水果 come first?
The 的 is not nessecary here as far as I know. Our teacher, who is a chinese, never let us use 的 in connection of a place. We could, it would be right as well but that would be more a written than a spoken sentence.
But is the word required in the sentence?
In this context as you saying it primarily links and doesn't mean "very"?