I have set the price to $19,99. I think it’s worth much more, but I have no experiences with selling on the marketplace so I don’t know where’s the “sweet spot” in price. I think this price is good for most people 
Creating a Mini Map like this would take at least 40 hours of work time (maybe 30 if you are really good with UMG and math), so I think $19,99 is actually pretty cheap for people who really need a Mini Map and is still in range for people who just want to play around with it or see how it works.