For a one man business and if the book keeping is in order, £300 to £400.
I may be wrong though.
I have always found an accountant worth the money in the long run but remember there are 2 types of accountants, a registered one and a chartered one.
Firstly it's important to have one or the other and secondly, a chartered one will cost a bomb.
Don't use an accountant who is not either registered or chartered. Whatever you do, make sure they are qualified and don't fall for the nicely said pitter patter from an un qualified one and I speak from experience because if there is a mess up with the taxman, the accountant isn't liable, YOU ARE.
Cheers