Okay I guess you're right. Iron prices would have to stay the same. So lemme make a suggestion:
IG spawners go for around 1.5 - 3 Million in shop? After all, they would still be considered the second best spawner in the game. The only one that's better is the Cave Spider Spawner.
But tbh, how does it break the economy? I mean, if you skyrocket IG Spawner price when the iron ingot price doesn't go up, who would buy IG Spawners from the shop? Right now on survival, you can't say that IG spawners arethat good. A full double chest of Iron Ingot only sells for 30k at the most, and a full double Chest of Spider Eyes sells for 220k.