Martin, the solicitor on this forum, I believe charges £3000 for a relatively simple not guilty, but then there would be extra charges for medical reports etc. You have to understand that even if you were found not guilty then you would only get a small proportion of your costs spent on your defence back. You can only put in a claim at the legal aid rate, which may be only 1/3rd of what you actually have to pay the solicitor.
Lose and the prosecution will claim £620 in prosecution costs from you, plus whatever they have spent on their medical experts.