I normally separate the kids from their dams at 4 days - when mine go for disbudding. Until then the milk from mum could contain colostrum, so it better for the kid directly than for me and cheesemaking anyway. So I would leave her on mum for a few days, but make sure she gets her fair share of milk (checking for full tummy, see if she is as contented as her brothers and watch when they latch on - i.e are they pushing her off?).
Will your kids keep their horns or are they going to be disbudded? If yes, then easy - take them to the vet and on coming home just try and feed a little bit from the bottle (preferably milked out form mum). It takes a few attempts and they may get quite hungry, but usually works by the end of the day. I would then slowly move her from mum's milk to replacer if you were to sell her on before she is weaned. Probably would take at least two weeks for that.
If she is going to keep her horns - leave it at least for 4 days, a week may be better (depending on how well she is getting on with feeding from mum, but 4 days is minimum), and then take her out of earshot from the dam, let her get hungry and slowly introduce milk. If you put her straight onto milk replacer this may be quite difficult as it is a completely different taste. Also make it up quite a bit more diluted than it says on the bottle, as otherwise likely diaorrhea. Temeprature is quite important to get to the same as it was from mum - again difficult to get right (drop onto back of hand or forearm, should feel slightly warm but neither hot or cold - if you have fed children it is easier to do.)
As to selling price, really depends on how much your feeding her on the bottle is going to cost - if you milk the dam - very little, if using Lamlac -probably quite a bit more... I am sorry I do not have any idea as to how much that would be, I milk my goats so costs don't come into it.