Typically if your implementation is 'done well', your labour hours should not increase and could in fact decrease.
However, that said, in some cases it could increase costs overall. For example, if you never recorded and tracked nonconformances before and you implement ISO you have a new resource requirement because you now have to have someone monitor and administer the system. Another more common 'additional cost of doing business' is Internal audits. Whether you contract them out (a direct $ expense) or try to do them in-house (a $ expense for training and then you have to add the person hours for the audits themselves), you will have an expense you did not have before your implementation.
I don't know of a rule of thumb (maybe one of the others knows of one).
Most companies do report decreases in manufacturing costs in large part due to better defined and understood systems (less wasted time), better communication internally, fewer nonconforming product incidents, etc., etc. I have seen various figures up to 20% to 30% savings (I cannot cite specific resource for these figures off-hand) within a year or two.
For data I can only recommend the ASQC's web site. Maybe the other folks here can help with specific citations.
QS9000 is a different story all together.