I live in Hampshire and I have at least three half marathons within travelling (walking in one case) distance that cost less than £20 to enter - Gosport, Fleet and Wokingham - all cracking races with a medal and well organised. I've not done Gosport but haven't heard a bad word about it. Fleet is fabulous and although I wasn't keen on Wokingham because I'd been injured and found it hard, I am doing it again. There are loads of 10ks that cost £10 or less (ignoring stupidly expensive races like the new sheruns event in Windsor - £22 and you have to show photo ID to get your number on the day, or spend another £5 to have it sent to you! I'm not doing that one!) and as someone has already pointed out, parkruns are free. I'm lucky in that Frimley Lodge is only 15 mins drive away, but when I visit my mum in Devon, I travel 45 mins to get to the one at Killerton (if you are reading this and live in South Devon, please start one there! - Stover Country Park maybe?)
I might give the Cardiff half a go next year as I went to uni there, but will make a weekend of it and it will still be a lot cheaper than the Cologne half I did in 2011.
Edited: 09/12/2012 at 20:14