Thoughts on effects such as unsummon or vapor snag?
If you want to run a bounce effect, most of the time it will probably be Winds of Rebuke or maybe Into the Roil / Blink of an Eye. The best option is usually Chain of Vapor, but the risk of Ezuri being bounced back is not worth it.
Master of Waves seems like it could fill the spot of Whirler Rogue. It loses the unblockable part, but could sometimes create 3+ tokens. Also easier to cast, and bonus pro-red!
I built this deck about a year ago, and started off with no cards over 25$. It still works, but you'll lose consistency/explosiveness. I have recently just bought a Earthcraft and added in the combos for it, but I did play it for about a year with out it. I even managed to take some games of other competitive decks. If your play group is casual, you can certainly do well with the cuts, and in my experience the deck was almost too strong for casual game play even without the expensive stuff. It can still combo off turn 5-6 pretty well. I'm adding in the more expensive pieces slowly. You can run a budget land base, mana rocks, and counterspell package to keep the deck price reasonable.
I've tried Panharmonicon, I think it's still to slow. Any fast mana you get early you'd want to dump into Ezuri to start getting counters. If you play this after Ezuri, it would probably take a turn's worth of mana, and for 4 you can probably drop 2-3 creatures anyways, getting you 3-4 experience counters. It would be good in a longer game where you end up just beating face with 19/19 mana dorks, but if it resolves it's almost always a prime target for removal. With the combo going off at 5 counters, I don't think its worth it. If you have a more casual build/play group, you could probably put it in for fun.
If you want to run a bounce effect, most of the time it will probably be Winds of Rebuke or maybe Into the Roil / Blink of an Eye. The best option is usually Chain of Vapor, but the risk of Ezuri being bounced back is not worth it.
Do you think any cards from Dominaria or Battlebond might make it in?
Merfolk Trickster, Saproling Migration, Spore Swarm, Spellseeker are cards I think I might try.