I don’t think your work is worth 1k as of yet. You have the basics of rendering down but you need to improve it before you star charging 1k for things like thumbnails. Also you have no examples of thumbnails and any past games you have worked for so where do you come up with the price of 1k? I think you should not charge for your work yet and just work on building up your portfolio and skill and then start charging as your work is worth 1k yet.
Try exploring composition, lighting creating scenes and backgrounds and posing.