Of all "low quality" fast food joints, Taco Bell is the only one I have ever found myself having cravings for on occasion.
It's easy to trick yourself into thinking it's healthier than other fast food (in a lot of cases it is, but not by giant margins depending what you get).
The 10 dollar challenge doesn't sound that difficult for a person of average size and metabolism. They have some pretty overpriced items these days.
I'm not sure what the parity of pricing between Canadian and American taco bells are these days, although I have access to both being in a border town. On the USA side though you have some items usually that we do not.
I say a big part of it is skipping the pop / carbonated beverage and just having water. It isn't taco bell that gives me a sore stomach when I eat there once in awhile, it's the giant fountain drink I inevitably end up with.