It can be a big thing, depending on your thoughts/beliefs about sanctity of life and potential life after death. Personally, I'd never feel comfortable doing it and wouldn't do it unless it was someone in extreme suffering who I knew very closely - but that's just me and years of Catholic school!
Is this someone known to you personally? If so, are they likely to be offended if you don't contribute? And are there other ways you can show your support, given you feel a bit hesitant about this atm?