Still, the only frames I'd buy from the market would be Mesa and maybe Excalibur if you chose wrong at the start. There's reasonable grinds, there's a few shitty grinds, and then there's Mesa, Excalibur, and Saryn. Chroma and Atlas are pretty bad too, but they're about as far from must-have as you can get. Saryn you can just ignore and go straight to her Prime until you get really desperate for mastery fodder.
Something to keep in mind, last Black Friday had a huge sale on just about everything (except plat itself, though they have done plat sales on other BFs). I'd try to only buy stuff you absolutely need (slots don't go on sale as far as I remember, and potatoes you really can't avoid) from the market, and only give plat to other players as much as possible. Even some of the vaulted primes are still way cheaper than buying non-prime frames or weapons from the market.