Those links aren't Manufactures though. They mainly provide to Promotional or Advertising Specialties. For blanks, they usually give you the price at the largest quantity. Unlike the Garmet Industry where we can buy from local distributors and really good prices.
I don't think it matters if you buy from one of those companies whether you're concerned about quality. You can simply ask for a sample, and make sure it's what you want. You just get less of a profit from it.
You might also try creating a Co-op and buying directly from a company that sells blanks.
Also, the PPAI association is probably the lowest cost for an association. It wouldn't hurt to join one. Like I said in a previous post, look in the Thomas Manufactures books or I think they may have a website called ThomasNet or something like that.