1) Don’t no-life the game to death. Play a mission or two a day and while your energy recharges go outside and do something else. Or play another game, etc.
2) Get crowns first from Jelly-Run or FSC, and build up enough to buy enough CE to do all the missions. Each run of Jelly Palace or FSC pays for itself.
3) Buy an Elevator Pass. It’s only $5 per month. Another way to look at it is an Ellie Pass is monthly membership.
4) Buy Energy. One pack of energy can let you do all the missions in one day.