Unfortunately you will still have to take the life in the UK test as you are over 18 and I assume there are no medical reasons preventing you from taking it. I would get a test booked asap as they sometimes have long waiting lists.
In terms of applying for citizenship, the Home Office current fee is £720. See link to current fees table - http://www.bia.homeoffice.gov.uk/britishcitizenship/applying/cost/
As from 6 April 2010, the fee for a single person to naturalise will be £655 (see table of new fees http://www.bia.homeoffice.gov.uk/sitecontent/newsarticles/2010/255022/20-immigration-fees-april-2010) so it actually appears that the fees will be decreasing in April. You may therefore want to wait and pay the lower fee though the Home Office do change the information on their website and so it is worth keeping an eye on this information as it could change between now and April.
I hope this answers your question in which case please Accept. If you require any further information, please ask.
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