My answer to those insane mana costs is to just spend blood.
Maybe it helps you a bit to find an answer to Expedition league's nerfs.
I also want to excuse myself for my accent and trouble finding words. Normally I write stuff down and take about a week to edit a video, but I wanted to bring attention to a potential good starter build as soon as possible.
The PoB to my character: https://pastebin.com/A5gj0XZg
Keep in mind, it is not a guide, but just a snapshot of my current progression. I started the character on Sunday and it is the third attempt for this league.