Custom Field adding cart value incorrect display frontend

[Coltras]

Adding a custom field to the product with a 'Yes' 'No' option and if they select 'Yes' it increases the price. The pricing on front end is with base price without Tax, the 'Yes' option is set to add £30 and when selected it does only add £30 to the base price without tax BUT on the option you select it displays '£42' which isn't correct as obviously £30 was added but i don't necessarily want them to know it increases the price, so would rather no price increase is displayed on the option text.

I cannot see a way to display actual value on the custom field without any extras. Anything i am missing or is this an oversight?