Please suggest a digital strategy to achieve lower cost per visit for a campaign?

in digital marketing cost per visit can be reduced by various ways, a few mentioned below:

SEO:

SEO Optimize ur website- Meta tags, meta descrip, alt tags.

Do an SEO Audit to identify gaps and then optimize your site.

E-Mail Marketing:

E-mail your customer base the promotion with link to the right landing page on your website( does not have to be the home page, rather the product page relating to the promotion)

Social Media campaign:

get your promotion out on social media - FB/ twitter

SEM:

Keyword optimization and selection- go for long tail keywords