6-Links cost too much to build

Those achievements are designed under the consideration of global trading.
Just do the Chaos recipe and buy one. Takes 3h max to get those 30c.

It's so easy to get a 6l chest that ggg increased the difficulty by releasing solo self found- modes and now ruthless mode.

If you had complained playing in ruthless, i would have agreed cause it's even difficult to buy one there.

Can't recall ever doing the fuse recipe, I prefer getting something I can use meanwhile, buying the chest I want and tossing some fuses on it on the side whenever I can. The average is under 1500 fuses so you get it earlier most of the time.

The stand-in is usually generic 6-link you can get for 15c that I rolled with a few essences, or, if I absolutely need a specific chest I'd 5-link it and buy another one to dump fuses on, very few setups actually require the 6th link to function.

Another thing you can do on the side if you need a unique chest that isn't too rare is get a matching 6 link base and chance-scour it. That's separate from alt-jewel-fuse so it doesn't interfere with your main linking effort, it's a total crapshot but you might get lucky. Of course, if the item you need isn't in high demand and you're fine with lower rolls, it can be the cheapest option to just buy it linked, well rolled ones can get pretty pricey since the divine change.

Got a small tip for painless converting currency, if you aren't in a hurry don't buy - sell instead, it's cheaper and people come to you instead of having to message 20 of them and get radio silence. When linking my current chest I sold chaos for 500 fuses in last batch, linked in 20 fuses and sold the rest, that's currency flipping so you also make a profit even when you match the best offers.

Strictly on topic, is 1500 fuses for a 6-link too much? I don't think it is, because it isn't the cost for just any 6-link, it's the cost for linking the exact item you need, that falls under optimization, and thus should be fairly expensive because it's an endgame goal.