Product price is shown without tax, but customfield is shown with tax

[V1llum]

Hi guys.

I am selling educational products to schools in Denmark. When you buy a product the price is 2000 danish kroner plus an annual licens pr school class of 250 danish kroner. Both of  these prices are before taxes.
On the product page, the price of 2000 kr is shown correctly.
In order to let people select the amount of school classes they want to purchase a license for, i have made a custom field (string) that shows up next to the "add to basket" button. You can see this on the attached screenshot. The problem is that i have entered the prices before taxes: 1 school class = 250 danish kroner, 2 school classes = 500 danish kroner and so on. When the price shows up on the product page, it is including taxes already: 1 school class = 300 danish kroner, 2 school classes = 600 danish kroner (since the TAX rate is 25 %).

The first screenshot shows how the prices appear in the customfield dropdown (prices with taxes).
The second screenshot shows how I entered the prices in the custom field menu in the specific product (prices without taxes).

So to sum it all up. Is there a way I can show the price  WITHOUT taxes in the dropdown, just like i entered them?

Thank you for your help,
Villads.