Depends on how much effort it takes you to do this. I would look to see if the site looks like it might last and get PR eventually. I would not spend much time trying to get such a link but if you can get it with a small amount of effort it sure could not hurt. Do you mean the site has no PR or the page has no PR. If the site has pr and the page does not that means it might just not have pr assigned yet and will eventually. At the very least you will get a tiny amount from anchor text from the link.