There was a German knife company, Herder, that went bankrupt / had a fire / can't recall the whole story. But for a while the market was swamped with blank Herder blades. Cheap. They mostly specialized in kitchen and utility knives, but perhaps you might find something of interest from them?
Similarly, both Schrade and Camillus went bankrupt about ten years ago and many blank blades were left over at the factories. Schrade used 1095 and 440A primarily, but other steels as well. Their 440A is on par with the 420 and AUS6 you mentioned in your first post. I prefer 1095 carbon steel over most of those.
Have you browsed the For Sale by Maker forum section here on Bladeforums? I see quite a few small fixed blade hunting and utility knives in the $100-150 range. Perhaps contact one of the makers and see what they'd charge for just a blade? Not many custom makers normally work in such low-end steel as AUS6, 420, or 420HC though.
Grohmann sells their blades as do-it-yourself kits.
Some Scaninavian knife companies make their blank blades available for sale. Helle, Roselli, Mora, Karesuando, Brusletto... You needn't worry about the quality from any of those. A finished knife from Helle usually costs in the range of $100-150, but most of their blades when sold for knifemaking are just $25-$35.
AG Russell had some unfinished Paragon knife blades for sale a while back. They're no longer available, but one might show up for sale at auction. The blades I'm thinking of were quality Japanese steel, and were designed by famous American custom makers; Tommy Lee and George Heron both designed knives for Paragon.
Good luck in your search!