That would depend on the weight of the caravan. My caravan is a 4 berth and weighs around 1,000kg, and I tow it with a Nissan X Trail that cost under £5,000. It's a great tow-car and could pull quite a bit more.
First you need to decide what caravan you want to tow, then work out what can tow it. You also need to consider how old you are prepared to accept for a tow car. Plenty of cars out there for much less than £5,000, but they will probably be older models like mine.