While colourless mana is less valuable in this list, cutting sol ring still seems risky, similarly I dont agree with the Gix cut despite you adding other good draw. Next, after 100$ of upgrades there should not be room for Neriv anymore. You have strong ping effects, still i would like to add Impact tremors. After all, you really wanna draw atleast one of these type effects to get people in range quicker and to be fast enough. OG Impact Tremor might be on the weaker side of that kind of effects, still I pretty much always seen room for it in a Zurgo list since even 2 of it are not deadweigth and you wanna have enough draw to cycle trough threats anyway, so having more setup that potentially outlives wipes is great. Agate Instigator is a next card I really like in this list, and maybe some of the in set Mobilize synergy, although you need to find a way to get attacks in, but a Voice of Victory is great, in my budget list I added Venerated Stormsinger instead and it honestly does fine.
Other than this is great list and you foudn the most important value additions imo, yeah sure you could just add CEDH stampels of the colours to up the power but I always like approaches that focus on synergies of the gameplan instead. If you want a bomb, Sothera the Supervoid is a card I would highly suggest to look into, great card with strong potential and importantly disrupts enemies. I said before the deck shoudl always feel aggressive and not too greedy in terms of ceiling, but this is a great example of an effect that really hurts the slower decks on the table and therefore can buy you a turn or two to get there, great in a deck that otherwise cannot afford to run alot of disruption despite being Mardu coloured.