At this point in time, I believe Instagram offers the lowest cost of entry. Leveraging hashtags to show up in search, following people, engaging on other profile posts, and posting to your own profile and story daily will grow your following as long as you put in the work.

Honestly, I would explore direct mail!

Influencer marketing. Find a bunch of micro influencers with sub 5,000 follower counts on twitter, insta, fb, snapchat and offer to send them free product. Maybe throw in a referral link and pitch them on the commissions they can make. The price being only your time to find them, communicate with them, your COGs, and shipping. Over time it can have a compounding effect on growing your brand while also driving immediate traffic to your site.

If you are acquiring customers it is ALWAYS great to have more products to sell to them. It's easier to sell to someone who has already bought from you. Expanding your product offering and selling those products to your existing customer base will drive repeat sales and go a long way to increasing predictable revenue and protect you from algorithm changes. Leveraging email marketing and properly segmenting your customer base will help you do this!