I have been to DLP a number of times in the last few years. Generally I go via Beauvais due to the vast difference in the costs of flights. Like you Vincent I have found the difference to be in the region of €500 for a small family.
Just back from a short break in DLP. Aer Lingus to CDG was < €500 for 2 adults & 2 kids. Does this mean Ryanair to Beauvais would have been < €0