It would be nice to be able to max out Temporal Circlets without going through the RNG.
This is what I think upgrading from level 6-10 will cost based on the values of upgrading from level 1-5.
Lvl 5 -> 6 = 26m + 60 Temporal Spell
Lvl 6 -> 7 = 50m + 70 Temporal Spell
Lvl 7 -> 8 = 98m + 80 Temporal Spell
Lvl 8 -> 9 = 194m + 90 Temporal Spell
Lvl 9 -> 10 = 388m + 100 Temporal Spell
Obviously, an exponential increase would feel bad, so mixing in some other materials like Powerful Dimensional Essence, and other Glast Heim instance related materials would be good as well. Hopefully, it should also be feasible for the average person to get.
Feel free to discuss alternatives and some number tweaking. Thank you!
EDIT: Added stuff