We Are Warriors $70
Just finished this one, pretty easy to hit the milestones without paying anything. The small gem pack with the first purchase bonus would net you an extra $0.50 but I didn't bother, the other two purchases would cost you about $20 after the payback, so don't bother. The gems purchases wouldn't really help you in the game anyway, you get plenty of them daily and they're for random card draws so it doesn't really guarantee that spending money will help you as much as you would think.
You can watch ads to double rewards after every battle, if you're selective about it (I developed a personal hatred for Atlas Earth ads) you can skip a lot of them and still use it to your advantage. You can progress through the timelines pretty fast, but I spaced out the progress so that I would hit the daily SB goal for each reward past timeline 4. If you don't want to worry about SB daily goals, you can probably get through a lot of the timeline milestones each day. If you want to hold back to use the timeline milestones to meet the daily goal, just get to battle 6 in the last timeline and then grind an event for the rest of the day.
It gets a little grindy and you have to play smart past timeline 30, but still easy to get through in the timespan, even spacing out the milestones to hit daily goals I still had over 2 weeks left to hit timeline 41