You have to seriously learn how to farm chests. I’ve been opening 4 - 5 chests per day for 4 months now (2 monster, 3 raid). For the last two months I’ve been tracking all my gems earned and spent from loots (titans, chests, MV, etc.) I collect an average of about 1000 gems per month and spend about 1150 skipping the wait times on raid chests for a net expense of about 150 gems per month. I’m also on VIP so I know I’m still adding to my gem balance over time.
I collected 13 non-farmable asc mats from chests in December and 7 so far this month. So for a net expense of 150 gems a month, this is a fairly good deal. It’s not as good as my titan loots but it does pay off. All you have to do is open a raid chest when you get a full set of flags and win 24 raids per day. When you fall short of that goal, it’ll eventually become a day when you only open 2 raid chests instead of 3. The gem cost should be around 10 gems when the cool down timer reaches 6 hours.