The cheapest item on the store is a sketch, at $2.50. The price is right, and even cheaper than the $3.00 one can expect for a lowest-tier microtransaction.
Given that it is the cheapest way of supporting the game, it will appeal to the greatest number of people, and will be the first store item considered by a new player. Unfortunately, not everyone has use for a sketch. It's not so simple as "Spend $2.50, get something in return" because anything we might want to apply a sketch to is going to require some amount of work in-game. Most of the customizable items require cloth or leather or rope. Cloth especially can be difficult to come by, especially in the early game. Why would anyone buy 5 or 10 sketches when they have only 1 or 2 items to apply imagery to? Why buy sketches at all if you are a newish player with no customizable items? I'm 3 weeks into this world with 5 toons, playing likely more than the average bear would, and still have virtually no use for sketches. Suggestion: offer something which is of value to all players, including new players, at the lowest dollar value, and place that offer near the top of the store.
This is something that should be considered. Provide a $3.00 microtransaction which does not require work on our part, and allow us to scale that tip to higher values if we desire. In exchange, provide us something of cosmetic or social value. Streamers have a lot of success accepting tips in exchange for access to their audience (messages and recognition, displaying the tipped amount and the tipper's name) and custom emotes. Compare your situation to theirs. Consider you have kept any sort of global chat firmly under your own control, which could prove a valuable asset.