Price will depend on shard a bit. Price for black would range from 40-70. Price for white would range 30-40. Depends a lot on shard, supply/demand. Cold resists can be a little problem but black is not too bad.
A super good blackie may sell for as much as 150-200 M depending on points, HPS and overall stats. I have seen a few blackies sell for 200 M, but different stats, also black is second most desirable color only to Blaze.
I also have see decent black and white Cus with super high hps just not sell at all.
Needing fast cash or running out of stable slots is also a problem. That causes us to sell for much much less, and in-game.
You can look in the Traders Hall under "pets for sale tag". and you may get some idea. Anyways best place to sell is in Traders Hall in stratics and not in game.
I would give it a shot at Traders Hall, and ask for bids, and elicit comments and offers. Probably best idea.