Basically, colour is governed by the types of flower the bees are feeding on, which in turn affects flavour. For example heather honey is fairly dark and has a very distinct flavour, but so does orange blossom which is light in colour. There are a variety of types of honey which can be extremely dark, sometimes called black, but these days people like to specify the main flower type (presumably to get a better price).
So saying black honey is not really very helpful unless you know the flora in that area, and even then it's hard to be certain. Some of the darkest I've seen is greek mountain honey, and perhaps holme oak honey we found in Spain. There are certain types of english honey which are really dark, but I can't remember which.
I'd just pick one with a flavour you like. :)
RE: cheap honey, dunno. My best guess is that the only risk is having more "unripe" honey content, plus more particulates and wax fragments which might increase cloudiness of finished product.
Just a few thoughs, hope they might help.
cheers
Pete
