Well...ehh...there are a lot better films that you could be pulling apart than the Saw films. They usually are haphazardly shot and poorly plotted. Also the first Saw film had a $1.2 Million budget and not a $500k.
If you want a really good example of a film shot on the Ultra-cheap and still looks great; try Primer. It had a budget of $7,000, unfortunately it has a plot that is convoluted enough to confuse just about anyone who sees it
Another one is Brick which is a damn fine film with a budget coming in at $450K.