English (UK) proof-reading of a Letter of Motivation (ca. 1000 words)

I am looking for a native English speaker from the UK that has excellent writing skills as well as experience regarding letters of motivation. The person is expected to proof-read a draft that I have prepared and suggest possible improvements. The letter in question aims at the admission to a postgraduate programme in law.

I am willing to pay up to £20, with a £5 bonus for a particularly excellent job.