You can look in the sales at similar horses, but we can't tell you prices here. (this post could be seen as advertising)

In my experience most people don't really like to sell DA horses, so you can always try listing it high and if if doesn't sell, slowly decrease the price.

this is an opinion question and not allowed.

Everyone has a different opinion on value, and how to price a horse. For those, it also depends on the design. You can try and look around at others and check their sales history to see what they recently sold for, although the history only shows the previous 90 days.

I'm going to lock up, because this forum is for questions on how to play the game, and there's no definitive answer when it comes to value.