I would budget at least double your cost, buying in that price range, and that assumes you are a proficient do it yourselfer with lots of skills. If you are not such a person, I would recommend looking at units at a higher price point which either have already had significant work done on them, or are new enough so they don't need it.
And yes, there are exceptions to every rule, you could fall into a sweet deal on a great trailer at a low price, or be burned with a real turkey rig, not worth close to what you paid for it.
There is no real answer to your question only generalities and opinions. Each trailer is different, along with each owner's expectations of what they will wind up with.