It all depends on the animal and the quality that you want the euro to be. I have had bears degreasing for 7-8 months and some only take 3-4, I have had deer take 2 weeks and some take 4 months. It takes a lot of time and dedication to get all the grease out of a skull. Truthfully, if you do it yourself, it will cost more than having it done by a pro, depending on their prices.
Skull Designs: Quality European Mounts at affordable prices