A Toyota Yaris Cross could be a good option. It has an excellent reliability record, and it should prove cheap to run, but it would only work if your caravan is braked—the braked tow capacity of the car is 750kg, but it can only haul unbraked loads of 550kg. Alternatively, you could opt for a Hyundai Kona, which still has a great reliability record and low running costs but can tow unbraked loads of up to 750kg and braked up to 1300kg, albeit with some variation depending on the version.