If you're after something reliable and cheap to run then a Polo or a Yaris is ideal. We'd also recommend the Honda Jazz and Skoda Fabia. For something different, you could look at a Daihatsu Sirion. Daihatsu is owned by Toyota and the Sirion is basically a Yaris underneath, so it's just as well built and reliable, but you'll get more car for your money. For less than £6000 you can get a 57-plate Sirion with less than 15,000 miles on the clock.