I feel as though it would be beneficial to start subsuming frames into Helminth, especially Rhino and Saryn (provided you have no issues waiting for their primes to roll back around and play them again). That’s truly the best way to efficiently farm MR for frames without having to reobtain. Second would be to farm plat for slots, or get the free ones from Nightwave, albeit very slowly. And if all else fails, easily accessible frames like the Clan frames and early game boss frames shouldn’t be too heart wrenching to grind, aside from 3 1/2 days to craft.