Suggestion:
Sell Profane, Green or Blue: Receive Brunts cash
Sell Purple or Orange: Receive Melks cash
I don’t think I’m the first or last to think the current currency system is out of whack. Parking up the 4 different currencies we have for a moment: Brunts cash is almost pointless past a certain point. I think I’ve got over 1m credits or something like that. It only goes down if I spam buy a weapon hoping for higher stats (whats that about btw? You’d never go in to a shop and buy a “random TV” in the hopes it turns out to be a Sony vs a Toshiba ~ no offence 
).
My thoughts are that the higher tier weapons, such as those sold by Melk (Purple/Orange) should be able to be sold to him; those lower that Brunt offers (grey/green/blue) should be sold to him.
That way: when I brick an item via upgrade I can at least get a few coins back. If I get an Orange drop from T5 I don’t want, I can trade for a few ‘orange level’ coins. And if I see an item in Melks shop that I think is worth it, in theory I can spend Brunt Cash + Plasteel + Diamantium to upgrade a weapon and convert it to Melks cash. It’d be expensive on resources, but it’d save you missing out on that once in a lifetime Recycler sword. Which incidentally hasn’t ever popped for me in over 400 hours of gaming 
- but that’s besides the point.