When I make my helmet and printing them take about 1 whole roll and about 3/4 of another one. And it also depends on how big it going to be but no more than 2 roll of filament. I also suggest to buy a Sidewinder X1 or the new X2 or cheap but reliable you can go for the CR-10
The easiest way is to throw files into a slicer and get an estimate of filament usage that way.
Everyone has different print settings for supports and some models are not well optimized for filament use to begin with so expect some wacky estimates if you ask "how much filament does a helmet take". Also if you're new to printing, expect failures and wasted material.
I would suggest staying away from Anycubic products. I will recommend a Creality CR-10 V3. Only downside to Creality is they do a really poor job regarding quality control. TinyMachines3D is a reseller of Creality and they do an amazing job of testing each individual printer and ensure it is working properly before they ship it to you. You pay a little more for this, but in my opinion it's worth it. Especially because their customer service is great. They also ship outside of the USA.