I found that most of those suppliers are just selling rebadged cheap filament from China (Aliexpress / Alibaba). This is the case with a lot of products, but it's really disappointing when these resellers are claiming to have produced their signature "premium" filament, which turns out is the same $12/kg stuff I can pick up myself from Ali... which is what I've ended up doing. Most of the time they're reselling Wanhao, or Winbo, or some no-name even cheaper stuff.

I myself ordered a few spools of Wanhoa from Aliexpress... came to $71.50 for 3 spools of PLA with Fedex 3-5 day shipping, which equates to $23.83 per kg shipped.

I also ordered a spool of ABS from IC3D (from Amazon), who now produce their own filament in the U.S. They have really good reviews, and at $33 with free 2-day shipping with Prime, seems a pretty good deal.