Decree Absolute legalisation.

We are getting married in Greece October this year, and the Greek authorities need legalised copies of our decree absolutes from previous marriages.
A notary wants to charge us £750 for the privilege!!!!
Firstly I don't understand why a legal document needs to be legalised with another colour stamp. Secondly ... can we get a court to do it ourselves.We have downloaded some d180 forms bit I'm not 100 percent certain these will bring the result we need.Has anyone else had any experience in this matter? We simply cannot afford that amount of money on top of everything else.