Originally Posted by
roskobosko
... (just marveling at the cost of that cage),...
I know people for whom the difference in cost between a $10 cage and a $50 one is not really worth considering. That there are things to sell to these people isn't much of a "marvel". It's fairly normal. It's also not targeting buyers of $10 cages.
Originally Posted by
roskobosko
... pretty sure I won't be happy with a bottle cage on my MTN bike, regardless of cost.
Good plan. A cage on a mountain bike would subject you to all sorts of social shaming.