There shouldn't have no profit from investment system...it's required a lots of labor and nonsense if you may not get profit.
We merchant just rise the price to earn~
And 60,000 per bottle isn't expensive...i think if it's 130,000 people would still buying it, but that would be newbie unfriendly.
And...if WP recycle too much zeny form this system, you could just increasing zeny earn like form BBs, many long and nonprofit quest.
Adding starsand or treasure box into investment or increasing OPB demanding are good idea too, although i personal perf rising poison bottle box chance