While 80% of the material may be supplied, material constitutes a relatively small cost compared to skilled labor.
Why not design your own pants? Woodland G3 pants are available to purchase. While they command a premium price, it's still much more cost effective than trying to get a proper single pair of pants made.
Labor's expensive even when lines are set up in an intelligent manner with some automation and a reasonable amount of throughput is achieved. One offs are expensive.
Properly making apparel requires a pattern. Getting a pattern made requires a patternmaker. For the sake of this post, a pattern is not a rigid template to trace on fabric. A pattern, CAD, is made using industry standard software like Accumark or Optitex along with a TDP to assemble to garment. After a pattern is made, a sample must be cut and sewn to verify specs. To get a sample made requires a sample maker. If the sample maker doesn't have automated cutting equipment, it's probably best to move on.
Sample, one off pants with multiple pockets, belt loops, pad pockets, etc, could be developed for around $2000-3000 after pattern and sample(s). Not including the pattern, just sewing a single sample would probably run $400-600. Grading wouldn't be necessary as you're only after your size. If you decide to grade and make 28"-44" waists, that will be additional. If the garment were designed using characteristics optimized for more generic machinery and cost effective manufacturing, costs all around could be greatly reduced. If you decide to go this route, you'd have an industry standard package to take anywhere for manufacturing.
Feed off the arm, hemmers, waistbanders, overlock, belt loopers, tackers, pocket creasers, pocket setters, etc, etc are relatively specialized machines usually set up for specific apparel. All of these machines require talented operators to produce a quality garment.
There are very few operations domestically who have the talent and machinery necessary to make pants like this in sample and short run quantities. If you track down a shop with the talent and equipment, they will charge accordingly and that's if they have any slots open. Once good sources are discovered, their customers rarely let them go and a year's schedule fills up very quickly.
ETA: misunderstood woodland MARPAT vs woodland M81(: