SEO is a term that many people know but do not understand yet. The base has been the same for years, but little nuances are constantly changing. Optimizing the website (internal factors) for many marketers still do well. Backlinks (external factors) still remain incredibly important and is a daunting task for search engine specialists. How can you still in a fairly inexpensive way of obtaining backlinks?

Of course you can contact other sites and ask to set up a link or cooperation.

One way to create your own backlinks is discovering expired domains, those buying and rebuilding the old site. Expired domains come because people have stopped maintaining their website or forgot to renew the domain. Often you can not buy a domain that already has backlinks and SEO value. For a few dollars you can buy the domain and purchase your hosting.

Through the Wayback Machine, you can then view the website in the old form. So you can download content, CSS and JavaScript., you can then rebuild the old site for your SEO purpose for your websites or your clients' websites. The you can add a backlink of your website. Note that you do this in a way that adds value. In sports clubs for example, you can add a logo under a new heading 

 "Sponsors".

This way of SEO and getting backlinks is not entirely "white-hat". So be picky on how to proceed, and construction certainly not back a hundred websites each month. 

 If you are not professional or don't have knowledge how to build recover website from archive.org. Then, you can contact the wayback machine downloader service provider by "Professional Services" these guys would help you get it recover site for you. 

Let me know if i can help you in this regard by commenting below.

 Good Luck...
You can watch video of the service provider before placing an order.