I had the same with an audience :D I still wonder how should one have enough tribute to afford 3151 in the first place (i guess only possible with modifiers on the tablets...which makes me reconsider the value of some of them). Also, does the game has a mechanic that those super expansive omens (let alone mirrors) only appear if you could afford to defer them have you saved up all tribute on the map... many questions!
Youre supposed to save all of your points until the end.
Every time you defer something it becomes cheaper the next time it shows up. You can also use tablet modifiers to lower the cost of deferrals