Comic grading from the UK.

I'm new to the grading side of the hobby and wanted to ask a few questions.

I'm likely to be using a middleman rather than going directly through CGC. The Subcentre look good but how can they get my comics graded with CGC at a cheaper price than what CGC would charge me to go direct to them?

Will I have to pay anything further through customs or taxes when they're graded and returned to the UK?

I'm only talking a few comics at a time... nothing massive.

Any advise or info is greatly appreciated.

Thank you in advance.