I sold a +3 poleaxe for a million (quite cheap, but quickly sold), bought a well-bred charger for 500,000, and now I'm working on looming it up to sell it.
At 500k, you don't really worry about upkeep. I have very few looms (Only gen 6. I play my alts a lot), but honestly I'd rather sell them to get more cash.
Try alternating between keeping and selling your looms for each gen.