If Im trying someone new, I keep it between the $3 to $6 range. Of course, much depends on their reviews on here, what their profile says, your own gut, and what their actual abilities are (which you will only find out after you try them). All my favorites are within this range.
I do agree that the cheapie readers are on Keen for practice or just testing to see if anyone calls them. Havent found a cheapie reader that had good abilities.