Hello~
I completely agree with what Beardo says and I'll see if I can offer some tips that others havent yet.
The first thing that popped out to me was that the girl in the full color drawing doesn't have any whites in her eyes (sclera)?
But for some artists that's an artistic choice so it's fine. Another thing that stood out to me was the lineart, not so much the actual quality of it since people have already touched upon that, but rather the coloring of it. It seems that you colored the lineart for her collarbones and her pants but nowhere else? It's a minor detail but consistency can bring a piece together so much better. Lastly would be the shading. You've used what seems to me to be at least 3 colors in her hair but the other areas only have 1 layer of shading. More layers of shading and/or highlighting can bring more dimension to the drawing. When choosing colors for shading, simply using a darker color of the base color isn't always a good idea either. For example, a lot of artists will never use gray as a shading color for white. It just looks bland. Rather they'll use a less saturated red/blue etc. Speaking of shading, I think the bottom half of the tank top could use some
I hope this helps a little, can't wait to see more from you!
EDIT: ah forgot about pricing. I'm no good at pricing things but I have seen artwork of what I believe to be similar quality selling for 300-500 bells here on tbt. Soo.... Take from that what you will c: