I know search ads get a bad rap sometimes, but I've been having a lot of luck lately. I selected only my most popular prints to show up in search (for what to promote you click "Specific Items in Shop" and then select what you want), and narrowed down the keywords to ones that come up most in the "keywords" section of my shop stats.
I've made 2 sales from it these past 7 days:
Spent: $6.08 USD
Impressions: 5,393
Views: 56
Favorites: 10
Orders: 2
Revenue: $30.00 USD
It really helps to be specific with them!