Yes. I love Rewarding Orb in Missions. Thank you :)
Undoubtedly I hate the Orb. However it seems like the game devs will keep it to the end, so I'm really happy with Orb in Mission.
I don't think missions cost a lot because the bonus now is excellent, the 4-star gems even appear in 3 hour - 8 hour Very Easy missions, and don't forget about Orb.
If you run out of money, you can fight in the Gold Chamber which opens every week, and you can upgrade the business shop, though it takes lots of time, but it's worth it.
Or you may try to skip the missions to find the Very easy ones, they cost less but the Hero XP is the same in every mode. Like in 10 mins, the Hero XP is always 16%, or in 14 hrs, the Hero XP is always 145%.
Ah, sorry. The 4-star gems drop everywhere in the mission. And the cost for them is reasonable, I think.