"[insert word here] mile" in a context like this refers to a stretch of road that may have some stand-out characteristic. Like a stretch of road with a high density of car dealerships may be referred to as a "motor mile". So a "bargain mile" is a stretch of road known for bargains -- shops that offer unusually good deals.
I went and looked up the source of the quote and from the full context I think what they're trying to suggest is that it's an area known for bargains of dubious authenticity or quality (shady), with an usually wide variety of items for sale (quirky).
For example, the article mentions a "$175 wedding dress". Since wedding dresses are more typically in the $800 - $3000 range, one that's going for $175 is "shady" -- it might be a fake brandname ripoff from some sweatshop in China, or maybe it was just stolen off of the back of a truck somewhere. (Shady could also mean that the area is dangerous and known for criminal activity but after reading the article I think it's clear they mean the merchandise is shady.)
Then the article mentions a 500 pound brass statue of Buddah. That's sufficiently unusual to qualify for "quirky".