So your saying you want to spend cantina NOT just on Characters & Signal Data, but you want to add R1-7 & R8-9 all to Cantina thus slowing down farming for Characters & Signal Data both.
I refresh Cantina 3x a day 365 days a year just to keep up with Cantina & Characters & I have 12.6mil GP.
Raid Mk3 is for R7 & R8 mats.
R8 is also great from Daily Crystal Packs every once in a while for 3200 & the monthly Relic Packs for 500 crystals.
R6 Mats is very easy from G12 conversion using several other store/currency sources.
As I said above, I'm not opposed to more Relic Mats, I'm saying pick something besides Cantina to add them.
Like Fleet, I only refresh it 6-9x a week & not close to the full 21x before the price increases.
Cantina is already in high demand & adding anything else will just slow down the process as a whole.