Each 1 kg spool of their metallic filament will only set you back about $54.
lmao - you wish !
it's 750 grams. But bear in mind it's 3times denser than standard abs or pla. So you only get a third as much for the same weight. IE: it's like buying a 250gm roll of abs or pla.
In equivalent printing terms it actually costs $216 to print the same amount that you could print with 1kg of pla or abs.

Add to that the fact that for large items you need pretty heavy infill as the filament is just too heavy and soft to bridge, and it's a pretty expensive material to work with.

That said it prints really easy and small items will print hollow with no problems.
It also requires a little more than just 'polishing' to get that metallic shine. You have to go through several grits of sandpaper and steel wool before you get close to metallic. For anything with fine detail it's a real pita.
In it's un sanded form it resembles a rough ceramic. Which is quite a nice finish by itself.

Nice helmet - but probably easier to print with pla and paint it with metallic paint.