The SEO campaign will help search engines (such as Google) to index the site, give the domain authority to rank the site in the top of search results.
An SEO campaign is a long process. If you are thinking of starting a campaign, our recommendation is at least 8 months and can reach 24 months for the best possible result.
SEO being a long process, positioning changes can occur after the first 3-6 months, but they can fluctuate a lot.
Prices may vary by project, we have a few standard packages, but if you want a custom campaign the question should be "How much will my SEO campaign increase sales?"