About the Lohnsteuerhilfeverein (=wage tax help association), they are non-profit organisations that charge according to your total income, i.e. the gross income before taxes and before applying possible deductions.
You have to pay a membership fee of 10€ when you first join.
For that you can ask them questions anytime you want.
Here's their charge table, taken from here:
So, if for example your income is:
50,000€ gross salary + 1,000€ interest income --> 51,000€ --> the fee for giving you tax advice and filling in the tax forms for you is 156€
Until May 31st, for the previous calendar year, i.e. 31. May 2011 for the income tax return for 2010.