My accountant costs me €520 a year as a sole trader and IMO its money very well spent.
The first year I used an accountant all my previous figures for the last 7 years were looked at and I was told about loads of things I should have been claiming & a couple I shouldn't have - the good outweighed the bad by a large margin though & I ended up owing nothing AND getting a hefty refund that covered the accountants fees twice over.
Now I find it removes a lot of stress from me & offers peace of mind having a professional do the job, knowing that its done right.
I also pay €200 a month direct debit to the tax man, so at the end of the year my bill is a lot less painful!