Don't know what 'not got a big budget' really means.. but if it's a grand or so, I can recommend the Vauxhall Astra 1.7 Diesel. That's what I've got, and it has a good boot, good room, quite economical and the CO2 must be good cos the tax isn't too much, comfortable too.
Got mine off ebay. I just messaged the seller to arrange a viewing and a test drive, then asked him what he'd accept. He knocked £200 quid off, although I did notice in the pictures, (and in person when I got there) that he lived in a huge house with a name rather than a number, with garages and lawns etc. I went from work full of paint, so he might have took pity at my appearance, but hey, it's worth a go.. psychology and all that.