Hi,
I’m also an artist so I understand you worked hard on these materials. However, you must understand that you are not selling for one or two people. Game developers spend a ton amount of time and money on their games but the pricing is always <$100 because their target customers are everyone, not rich people only. You’re selling these materials for everyone, not studios so that the price must be reasonable. I’m pretty sure your sale will increase if you make an affordable price. I love your materials so I spend time to write this suggestion 
Good luck!
p/s: Is it possible to change the color of your material?