I think you'll be hard pressed to find a very wide selection of high quality <$10 powder coated enclosures with a quick turnaround anywhere. We overcome a handful of challenges to offer them, I'm sure LMS or other USA based parts suppliers run into their own unique challenges.
-Stocking bare enclosures is one thing. I can stock a few thousand of those at any time, "easy". We powder coat seven enclosure sizes in 11 colors. With the bare +11 colors, that's 84 SKU's of enclosures we have maintain stock of, a lot more to juggle than 7 SKUs. We try to maintain 1-4 months of stock at a time per color, but we do run out of stock frequently as demand changes frequently. We choose to only sell what we have on hand (versus pay-and-wait) so we aren't sitting on anyone's money while you wait to get an enclosure to get colored.
-Then I need a place to store all of our stock. Every new color requires another shelf. At the moment we are maxed out space for enclosures in our small warehouse so offering more colors poses a real estate problem.
-Cusack (our powder coater) will do batches as low as 50pcs. However, they are much better set up and prefer batches of 100pcs+ because fixed setup/teardown time takes the same amount of time whether it's one enclosure vs 100pcs. So we opt for larger batches to optimize efficiently. Their lead time is somewhere between 2-6 weeks. So that must also get factored in with the stock we have on hand.
-The powder coating process is expensive. It's a lot of equipment! Enclosures need to be cleaned, powdered, then baked. Powder spray guns and their lines need cleaning every time a color change happens. Plus there's a lot of equipment including a large oven a person can walk into that needs frequent maintenance. On top of that, the people powder coating need to be paid! We're doing this in Michigan! Powder coating is an art, too. It takes time for the artist to learn the connection between equipment and the powder. Powder itself is relatively cheap, but the whole process it's quite expensive.
All and all, I sympathize with you and all the DIYers out there. I wish we could offer 100 colors for $10, that would be sweet! At our scale with the logistical challenges presented, we cannot.