I think 50-60k would be a good base price. The color change is flawless, and the body prep looks amazing.

The hair base looks really good how it is, however, I would probably work on adding strands/highlights to make the hair more detailed. There are some good tutorials on DA and in the "resources for improvement" topic in the Art Help forum.

The lighting looks a little off. The highlights on the horse's flank, stomach, and shoulder look a touch too bright, because it doesn't look like there is a light source that would make those highlights. I would make those a tad darker.

And finally, the grounding. The horse's back hooves are kinda... tipped forward? Like, if the horse was actually in that position, he'd be airborne. I might rotate the horse's right hind hoof so that it would be a bit flatter. Also, I would stretch the shadow toward the left, because the brightest light source is on the right.

Overall, I absolutely adore the piece, and I wish you luck on your art journey!