I dunno, maybe five to seven bucks for enough for both wheels. Not as cheap as electrical tape which most of us probably have on hand anyway, but IME electrical tape's adhesive gets gummy and loose and just sorta gets to be a hassle after a while. I say this as someone who has had to fix way more than my fair share of flats due to once living in goathead-ville -- when pulling the tube the elec. tape would often come with it, and that's just adding a minor insult to injury...

If you only have to fix a flat once in a blue moon then electrical tape probably won't ever be a problem as long as it stays lined up right when reinstalling the tire, but good tape is something that requires no further consideration unless you need to get under it to fix a spoke or something.