I wouldn't buy that potion even with a 95% win deck. Simply because i hate giving away cards with a potion i buy.
It is obviously discouraging (for me at least) to use a potion that will benefit the opponent or has a chance to benefit him while not benefiting me at all and in fact using up from the charges when loosing.
Also not sure if your records will clearly prove to you this, but i have a treasure battle potion i keep there since set 3 or 4. Why? Back then the most loses were from returns and i seriously wouldn't want to risk rewarding players who play them. Not even today.
Nowadays i am too carefree when playing. Either way i still don't have a reason to risk rewarding the opponent with my own potion, whatever deck they might play.
I didn't buy the potion. It was some event promotion. So you can look back to when the potion was given out and then conclude for how long it's actually sitting there, since my estimate could be wrong.
Give me the most expensive treasure battle potion for free or even a far more powerful one, i still won't use it the way it is!
So instead of asking about the price, i think it's better to ask what kind of potions people would like to see!
How about a potion that gives you a point card every 10 games? Regardless of the fact that it's a draw / win / loss in order to encourage absolutely all players to buy it.
Or even a potion that merely gives you some extra free lotto draw every 10 games or more. Up to you. But that's a potion i would probably buy if i were keen on any potions.