Mausoleum Of The Emperor:
Both players can pay lifepoints equal to the number of monsters need for a tribute summon x1000, and Normal Summon that monster without tributes.

Spell Economics:
You do not have to pay any life points to activate a spell card.


Can I use the effect of Spell Economics to negate the life point cost of Mausoleum?

No you can't, Spell Economics lets you skip the payment for ACTIVATION, Mausoleum is not payed for activation, its part of the effect.

Not to mention it only prevents payment for activation upon immediate activation from the hand...

Things like Field Magic Cards or Continuous Magic Cards do not count...

"While "Spell Economics" is active, you don't have to pay Life Points to activate a Spell Card (place it face-up on the field), but to activate an effect of a Spell Card, like "Archfiend's Oath", you still have to pay."

Only things like...

Confiscation
Delinquent Duo
Dimension Fusion
My Body as a Shield
Enchanting Fitting Room
System Down
Toon World
Final Countdown
etc
etc

...would become "Free" from cost