From my understanding a cheap cob can be less than half as good as a good/decent cob. Basically, to get the same growth you will be running near 2x the watts and heat just to save what, 20-30% of the build cost? I mean, you will still need a driver and heatsink (possibly bigger heatsink) and all other minor cost parts. If that's the route you;re going, why not just take less risk of poorly made cobs and just use HPS/MCH?
I'd suggest buying mid grade cobs before buying trash cobs... Buy somthing you know lights up. I believe you can get cax3070s (top bin) for like 15$ off kingbrite, that's like 60$ for 4... That's a 240 watt possible light for apporx 200$. Again, if you buy 2 dollar cobs it might take you 8 to get near the same growth, double the heat, double the watts, more heatsink and who really wants to grow under blurple?
I don't know much about other Cobs but Citizen look good too and are way less $$.
You don;t HAVE to grow with CXB3590's top bin to grow extremely well, it's mostly for efficiency at that point and really only slightly better in the end.
Feel free to correct me if I'm wrong.