How to reduce the price of units batch ?

Hi all,

I’m working on a store with Woocommerce.
I want to sell t-shirts (for wholesalers). I want the ability to order 1 t-shirt or many t-shirts. But I want also put a different price per boxes of t-shirts.
Better with an exemple : a t-shirt costs 1.20€, a closed box contains 50 t-shirts. If customer orders 50 t-shirts, it costs 1.20*50=60€. Easy. But if he orders 30 t-shirts (I have to open the box to take 30 t-shirts), I want to add 3% to the base price if it is not ordered in boxes of 50. So here, it costs (1.20+3%)*30. And if he orders 80 t-shirts it will costs (1.20*50)+ (1.20+3%)*30.
It’s a sort of incrementation…
Another difficulty : I can’t set a value on the whole store because for one product it would be a box of 100 tshirts, for another a box of 250 tshirts etc…

Can a plugin do that ? And which one ?

Thanks a lot !

Jean-Baptiste.