As RobsLuv already stated, if it's a spousal sponshorship, then there is no minimum income requirement. You don't have to prove means at all. It may have been different 3 years ago, but that's not the case now. If the PR goes on welfare during the 3 years though, the sponsor is responsible for paying it back to the government. The sponsor will need to provide an Option C or whatever it is with the application to show they're not on welfare though.
Sponsoring children or other family members it's different though from what I've read and you do have to prove means.
Edited to add:Found an explanation on this website:
http://www.settlement.org/sys/faqs_detail.asp?faq_id=4000444If you are sponsoring:- Your spouse, common-law or conjugal partner who has no dependent children, or
- Your spouse, common-law or conjugal partner whose dependent children have no children of their own, or
- Your dependent child who has no children of his or her own,
then you do not need to demonstrate a minimum income.