Impossible to answer. You can buy a cheaper caravan that has been regularly serviced, damp free and in pristine condition. You can buy a more expensive on that turns out to be a real dog, and vice versa.
I would spend time visiting dealerships to look at types of caravan, layouts, prices etc then start to refine what you actually would like. One advantage of a dealership purchase is that you get the protection of the Consumer Retail Act 2015. Plus if you use a credit card for part of your purchase you get CCA Section 75 protection. Or a loan taken out via the dealership gives further protection. For a private purchase you get virtually no protection if things go awry.
What car do you have as this will define to a large extent what caravan you can tow.