i have this site [URL REMOVED BY MOD] I came to know that 10 power backlinks are better than 100 backlinks from sites having PR<=3 . . so now where can i get these power backlinks in free of cost..?
In the vast majority of cases you aren't going to find people with authority sites just passing out backlinks to you. You can purchase some high quality backlinks in the BST section. I'd recommend starting there. Still, don't take everyones word, do your research when looking at the sites you are going to purchase backlinks on. Make sure OBL is low, it is related to your niche, and that it meets the criteria you are hoping for.
You could also offer to write a post on a authority site in exchange for a link, in fact your find people in the BST section offering you a link for a blog post.
If I were you I would build another few websites , and after a few months you can get PR3 , And than link to yourself . This is the best and cheapest way .
getting the links for free will more than likely not happen. You can contact college clubs and offer a "donation" for a link from their EDU site. Expect to pay over $100 for that though. You can buy sidebar links in the Link Sales board on DP You can guest post but the return on that will be low. You will probably get a response rate of 20% or less. Meaning if you send 100 emails you will get about 15-20 responses.
Guest posting is a good option. If you are a quality writer, you can go out and contact blogs and ask them if they would like a high quality article for their site, and in exchange you can add a couple links in the author bio.
You can try guess blogging, it is one of the best way to get quality link If you willing to spend money, buying link is another fastest way
You should submit your articles with your link containing your keywords to some article databases such as EzineArticles, Helium or ArticleCity. It can bring you traffic and you also get link from trusted domain.