+1 on wot darrellm said.
If you go for a cheaper one can kit, go for a 1.7 or 1.8kg can, unless you want to brew short, in which case 1.5kg is fine.
Coopers have a good one can range and the yeast is reliable, although I found that the John Bull IPA and Traditional English Ale were better than their Coopers equivalent. There are several lighter beer Coopers kits, but they may come up a bit bland, apart from the Real Ale.
I have found that the darker beers need longer conditioning than the lighter ones.
All of the one can kits will need Dried Malt Extract or beer/brewing enhancer. Don't use table sugar.
If you want to just have a go on the cheap, you could do worse than a Wilko Hoppy Copper Bitter plus a jar of Holland and Barrett liquid Malt Extract and brewed short to 15 litres. This will come good after about six weeks conditioning and will be given a lift if you dry hop with an English hop like Goldings.