PR is only useful if you get press features. Odds are you won't, so go with ads every time. PR is too good to be true, kickstarter campaigns are too small of a thing for the media to cover, in general.
There is no such thing. You are like asking for a cofounder and usually cofounders you share the profits and company with because they are sharing in the risk. What you are asking for, is for an employee to work for you for zero dollars upfront - and they share in the risk - and in exchange if thing...
Don't set your reward delivery too fast or kickstarter may take notice. Set it out for a few months, and then just ship it right away so that everyone is pleasantly surprised.