Yea renting will be really nice. I've built up my collection over ~2 years of playing, so I'm able to play a decent range of decks. I don't have the crazy expensive cards though like Thaeriels or Demos.
FYI there are older zombie lists that are even cheaper. Necroscepter is the most expensive card in those lists at ~$5 each. It's definitely possible to work up to those cards just from daily play and earn.
Interesting list! If you check my last post (https://peakd.com/@kstreet/competitive-zombies), that deck is a very similar idea: it plays differently into aggro and control. Even changing god power. I'd say that the list I posted leans a bit more into aggro creatures where this one is more focused on the combo. Both should be fun to play.