I think you should avoid to buy backlink. Its very high risk since Google algorithm update. If you wish, you can optimize your site to getting backlink naturally. For this, you can write useful article for your visitor, and give best information for them.
Just use the off-page optimization techniques to build links to your site. It is free from search engines, No need pay any thing, Do as manually.
Dear....you should not buy paid links which is against Google Guidelines and penalised by Search Engines..You have to create quality backlinks by Effective Off Page Optimization like Article Submission, Press Release, Forum Posting, Social Bookmarking...Best of luck