Selling Products by Weight in RapidcartPro

hi there, I want to sell our cheese-products and i created a product-database in RCP4

My product has a “version-price” of €10,00 per kilo
The customer must select how many grams they want to buy and can choose between 250, 500, 750 grams or 1 kilo.
I’ve created an optionlist that is called “weight-list” and have the weights entered in the options-list.
i’m calculated every weight-choise to their right value ( 1 kilo = €10,00. 500 gram = €5,00 and so on)

Is there an method or option to calculate the prices belonging to the weight-list automatic?
At the moment when i’m changing a product-price (from €10,00 per kilo to €11,00 per kilo) i must recalculate every option by hand and
that also for my complete product-database. That can’t be the right method i think??

Is there an syntax for that just like " ( [product-price / 100] * selectedweight ) "

Thanks for your help.