First Commander Deck (Miirym)

I've never played commander before, but I promised my son I'd build a commander deck to play against him. This is what I came up with:

https://moxfield.com/decks/7s8zoxfYtUCl9QP0zBdPaQ

We already have over half these cards. The most expensive card on the list I have yet to buy is [[Terror of the Peaks]].

I welcome any suggestions and tweaks,and while I know certain expensive cards like Klaugha, Cavern of Souls, etc.. would help immensely, I'm trying to finish this deck on the cheap cheap.

Thank you.