If you're looking for anything on the cheap while in the Hong Kong area, your best bet may be an area called Mong Kok in Kowloon. One of the most densely populated districts on Earth, Mong Kok is home to various markets, from streets that chirp solely with caged birdsong to avenues laden with athletic equipment and bathtubs. Ladies' Street is where you'll find food vendors sharing their turf with booths of feminine products (not the most alluring of mental images), with plenty of quick food to choose from for under $2 USD.
Be warned, this place is high energy and chaotic, no matter what time of day, so if you're one to lose it in a crowd, find your quick eats elsewhere. If you want cheap electronics or sneakers and a snack like fish balls or roast pork or fried squid or... you know what, folks? We have a better idea. Take a walk through the market and check this stuff off of your own list!