It really depends. If your site in a less competitive niche, you will need a few backlinks or even no backlinks at all. Some of my new sites do not have any backlinks and they still rank pretty well on the Google. I really think that backlinks are still important but are also becoming less and less important, because the search engines are becoming smarter and they can be bought, fakes very easily. So the less competition you have, the less backlinks you will need to get traffic from the big Google.

If you do not have to get results faster, you do not need to pay for any SEO services at all. Keep in mind also that quality services are always expensive and cheap services will do more harm than good.