The Light Monkey 3W is a phenomenal backup light, but as far as I know does not come in a 2 C cell configuration like the OP is looking for. They do sell the Light Monkey 2W, but that takes 2 lithium CR123 batteries, rather than 2 C cells.
As far as my research goes, you've pretty much got the list. I wouldn't call Halcyon or Heser cheap, but I can tell you that I know plenty of divers who have been happy with both. Heser seems more affordable than Halcyon in Europe, and vice versa here in the USA.