Before this thread gets too old ...

I took another look at the Stanley Classic Retractable Blade Knife, rather than one of the newer folding versions. The advantage of the retractable knife is that you can choose to have very little blade showing, enough to cut through tape and open a box, but not enough to damage what may be in the box. With a folder, you get the full cutting edge each time open or closed, all or nothing.

Cheap at less than $5, but uses the same utility blades.