There is concept that floats around in the business world that I always like to employ for Costuming as well. It's the Time/Cost/Quality Triangle.
Basically, it boils down to, you can have two of those concepts, but not all three. You can have a costume quick, but it is either going to be very expensive or very low quality. You can have a costume very cheap, but it is either going to take a long time, or be low quality.
Paper based Pepakura and Foam Based Pepakura are both skills that can be easily learned, if they do take time to master. Take some time to research and look around here on the forums at both to get a better feel for them. Pepakura can almost be a "Build BY Numbers" system, but paper based Pep will need the use of Fiberglass and Resin, or another strengthening material and Foam requires a unique set of skills to make look really good.
Unfortunately, since you have picked Felix, that is going to be Halo 4 armor, which is inherently much more complicated to do than the "Original Trilogy" armor.
Here is another member that did Felix armor to get an idea of the process:
Ok so I actually built a scout helmet for the fun of it back in February last year Then late 2017 I got the idea heck why not use it for a Felix cosplay Bodysuit and pouches arrived! Con photos Thanks for checking out my build :D A big thanks to...
www.405th.com
ANd here is the netry in "The Armory" for the Halo 4 Scout armor, if you want to have a crack at Felix's helmet as a start:
This is a comprehensive zip file including numerous files from multiple artists. Contents of zip-file: halo-4-mjolnir-gen2-scout-sarah-palmer-boot.pdo Modeler: Master Builder Ripper: @Arcanine halo-4-mjolnir-gen2-scout-sarah-palmer-chest.pdo...
www.405th.com