That is a typical cost for the last building. Be warned Welcoming Alice and Welcoming Queen of Hearts are going to be very expensive as well. In the Lion King event Simba was 12,500 EC, and Scar was 15,000 EC. In the Aladdin event Genie was 16,000 EC and Jafar was a whopping 35,000 EC.
This is why I've adopted a strategy of upgrading my characters as long as the upgrade is 1000EC or less (around Level 6). Once it goes over, I don't upgrade willy nilly. Upgrade if it's necessary for a task, or if my EC is high enough that I know it won't impede my ability to welcome those last two characters or get as close to the 80K mark for gem conversion as I can.