The list mentioned has a fairly comprehensive list of vets that funsters have used so that you can make a choice from comments posted. You have five days to do this and must be more than 24hrs before you sail so Calais may not be your only option. I hope that helps
We used the vet in Le Mailleraye sur Seine in May tel no 0235053767 to book an appointment vet speaks English its just up the road from the aire which is 5 euro a night.We paid 15 euros plus the tablet :thumb:. You are about 160 mls from Calais.
GPS N 49.482021 E0.772677 for the vet opening hours Monday to Friday
8.45 to !2.30 and 15.00 to 19.00 Saturday 9.00 to 12.00
If you go to the map in downloads and cluck on a vet it'll give you phone numbers, cost etc...
It's further south but the vet in Allencon ( street with the Dutch name) charged only 15€ per dog including the tablet. Year before a vet somewhere up on the channel coast charged me €63 for 2 dogs, so worth checking.