To save money on food, eat at local eateries. Anything 'western' is going to cost more. Eating local is the way to get the best bang for your buck IMO.
As for driving in HK...not advisable, it will cost you a bomb, gas is four times as expensive here and traffic can be a problem...public transport often works out as fast or faster than driving! Streetside parking is almost non-existent too.
Some of my friends have stayed here:http://www.yesinn.com/