I personally would not go as high as 200 for something that I am not sure will sell.
It does depend on your suppliers MOQ, with suppliers I deal with it tends to be anywhere up to a case which is normally no larger than 36 or 48 units. I would therefore not order more than a case to see if it sells and if it does then order more.
If it is a private label then I would go as low as possible, if the MOQ was say 50 I would just buy 50. You can always buy more if it does sell well.
Obviously there are many other factors such as you may get quantity discounts for buying more items which makes it more profitable, how much money you can afford to tie up.
Also in cases like this it is good to have an exit plan if it doesn’t sell. Can you get the stock returned to yourself, how much would it cost? If you can’t get it returned how much would it cost to dispose?
I have always believed in buying as little as possible for a new line to get the feel of whether it sells or not.