I have been working on SEO for quite some time now and I have seen that the key is to get one way backlinks (not link exchanges) on high PR websites that are related. If you have a website about hamsters, then you will want some links from pet related sites because this gives you some credability.
Try to concentrate on high PR pages and find out ways to get backlink with dofollow attribute to your site. Either link exchange or purchase or anything it does, getting a dofollow link from high PR pages will definitely give a boost in your PR.
Yeah, not bad idea, but i have invest in the GOOGLE AdWords,so i have no extra money to pay the serviceï¼May be later!