Hi pineapple,
I am doing research involving focus groups as well. I do not pay participants anything, although I think a incentive is very important for people to attend / partcipate (e.g. "education points", "tea/ coffee/ biscuits" etc.
I have been to groups myself were participants were offered a meal and been to one study where you got 30 Euros if you filled a questionnaire.
Not sure regarding payment and ethical issues. I think, if you pay at all, this should only be a very small amount.