You should give something unique but inexpensive to make for people who actually create one of your designs. For example, the channel wakethief gives a unique but simple "power pumper" hat to anyone who sends them a video pumping their foil longer than a minute.
Assuming you have a 3d printer and an old phone, the parts alone will cost around $450. so you can make an estimate yourself. I don't have plans to sell a fully built one yet.
