Custom field problem

[Vejgaard]

I have a small problem.
I have a product that costs 450 DKK. It is there to choose another version which costs 100 DKK more.
So I added the Custom fields a field that makes it cost 100 DKK more. The problem is the throw VAT on so it costs 125 DKK.
If I put the price of 80 DKK then throw it the 100 DKK on but customers sums do not throw the 100DKK when it says 80DKK Something I can fix so it takes VAT in the 80 DKK?

http://shop.sportscentret.dk/rulle-skojter/ekstraudstyr/hjul/rollerblade-in-line-hjul-komplet-m-lejer-og-spacer-detail