Cheap, fuel-efficient automatic car

I’m currently working towards my practical test. I want to buy an automatic car to just take me to and from work and maybe go on a date with the missus to another city once every few weeks. I don’t earn much and I don’t know anything about cars.

What would people recommend if I wanted an automatic car that is cheap to buy, fuel efficient, low insurance costs? I don’t mind buying a used car and it doesn’t need to be fast. Just want something that will be cheap, reliable, and won’t be a headache.