It's worth noting that people have made the case for no Black Lotus in Workshop decks in the past. I'm not personally a fan of the argument, but you wouldn't be the first person to top 8 vintage champs with Lotus-free Shops.
On the other hand, I wouldn't take a stock shops list and cut Moxes for Opals, it's going to be ugly. Note that Mox Opal in particular is basically only good in decks that run the five original Moxes to get metalcraft faster. I really don't think you'll have much success if you just swap out moxes for other mana and leave everything else the same ... But I think there are some more creative things you could do.
When I'm building a deck with limitations, I try not to run bad versions of more expensive cards, and rather look for opportunities ... in what way can this limitation be a strength?
No — it does nothing
For starters, cards like Arcbound Ravager explicitly synergize with Moxes and get a lot worse without them. But other cards, like Null Rod, are better when you don't draw Moxes. A lot of the cards that are particularly good with Ravager, like Walking Ballista and Hangarback Walker, also get a lot worse with a Null Rod in play.
If you can find a way to build your Workshop deck to operate under a Null Rod, you might be able to do some real damage in a mirror match, and probably end up with a better matchup against Outcome decks than a stock Ravager Workshop deck has. My gut instinct is that Null Rod either puts you on some kind of prisony Smokestack/Crucible of Worlds/Ensnaring Bridge build, or something real aggressive with Chief of the Foundry/Porcelain Legionaire/Traxos, Scourge of Kroog.
Cut Moxes for Utility Lands
Mutavault, Karakas, Ghost Quarter, Inventor's Fair are all cards that Ravager Shops would love to run but can't fit. You can even go deep with things like Buried Ruin and Tower of the Magistrate.
Cut Moxes for Depths/Stage
I haven't thought much about how you'd build this, but it has to be nice to have reasonably fast, uncounterable win condition in some matchups. Consider Expedition Map as one drops may get better in a deck replacing Moxes with lands.
Cut Moxes for Bazaars
It ain't budget, but it's cheaper than Moxes and it gives you an idea of how to think outside the box. Dredge Shops deck @Oestrus played in the VSL recently is a deck that runs Workshop and doesn't really need Moxes to operate. Any deck that wants Workshop just for powering out a single lock piece on turn one is in the same boat.
Cut Moxes for Mountains
If you're dropping Moxes and Ravagers, you might have enough room to add nonartifact cards to the deck. Classic workshops decks were 5 color or mono-red and made heavy use of Goblin Welder, a turn one play that might be nice on your mana curve. You might be able to explore other options as well. Thalia, Guardian of Thraben? Fastbond/Crop Rotation? Disciple of the Vault/Vampire Hexmage/Urborg, Tomb of Yawgmoth? Cutting artifact mana means you have access to options other workshop decks can't even consider.
Cut Moxes for Eldrazi Temples
This is my favorite. Moxless budget Eldrazi is an established archetype, but I think there's room to explore on the edges. Because Eldrazi Temple is an accelerant, you miss the Moxes a little less. My favorite thing about this? You don't even need the 4th Workshop. A while back I was working on a Workshop-Eldrazi hybrid deck for a potential post-Workshop metagame, and I found that 2 or 3 Workshops was all you wanted, 4 was just too many. I was playing with Moxes but I'm betting there's a build without them. You end up with a deck that feels very much like Workshop Aggro. You have less synergy and your mana is clunkier but your individual threats are bigger and more resilient. If you can find a way to make this work Null Rods and Thought Knot Seers, I'm guessing you'll end up with list that's even better against Outcome Combo than stock Ravager Shops is, and pick up a few free wins against players with more Ancient Grudges than Swords to Plowshares