The patterns for the Halo 4 and 5 tech-suits are not free either. When I said "freely out there," I meant that someone has taken the time to create the pattern and sell it to individuals or license it to various websites, not that the file itself was available for free. The cost of the use of that file is incorporated into what the various sites charge.
Now, if you do look at the various build threads I linked above for other member's Reach under-suit builds, templates were used for the sewing or foam construction. If you wanted to pursue he option of making your own morph-suit based under suit, you could use those same sewing or foam tempaltes as the templates for painting it yourself onto a base white or black suit.