How much extra to charge for OPI GelColor with a mani/pedi

[Boop]

Hi,

I want to encourage people to have OPI GelColor instead of regular polish after a manicure or pedicure.
How much extra would you charge to 'upgrade' to gelcolor?

My manicured are £14, £22 & £26
and for OPI GelColor I am charging £26, with an introductory offer of £22.

All ideas welcome

Thanks

 

[Boop]

forgot to say that with a set of GelColor, I will be shaping & doing cuticle work etc