Supplemental COB under $250

looking for the best bang for my buck to finish off a 4x4 flowering tent light setup. I'm running a 400w ceramic metal halide and a 450w (150-190ish equivalent) led

I'm looking for something to add in adjacent to or replace the led.

Budget is under $250

Take a look at timber grow lights.

Northern grow lights has the quantum boards

I'd look to build two bars, each with two cmx22. You could place a bar each side of the metal hallide.
like this
https://www.rollitup.org/t/citizen-led.928908/
except with these cobs
http://cobkits.com/product/cxm22-light-engine/
2 x these drivers
https://cobkits.com/product/meanwell-hlg-120h-48a/

thats $120 for each bar. Add, lets say, 30 in accessories to give a total of (120 + 120 + 30) 270. You'll have two very flexible fixtures.

(quantum boards are also a great option)