Well there getafreelancer.com and http://forums.deviantart.com in the job offers forum if you sign-up and offer the job with specifications im sure you'll get a great designer. They're always getting people to jobs from there. Jobs anywhere from small personal sites that are about 12 GBP to about 1600 GBP. Its mostly done in USD there on the forums but a lot of the designers to come from the UK themselves. I trust them very much. Lots of them have impressive portfolios to look at too.