http://www.amazon.com/Alliance-Antimicrobial-Rubber-Inches-42199/dp/B0017TPZNU
^450 bands for $4
http://www.dykemarubberband.com/specialty_rubber_bands.php
^1,750 for $8
Unlike what R.K. Magician said, the reason they're stretchier isn't just the fact that they're non-latex. That's just a plus. These bands are originally designed for hospitals and are mass-distributed to them due to their high-quality and latex-free properties. A box could last you a while, yes, but if you're getting serious and plan to do busking/table hopping with them, get a bag. Bands go by quick, and don't bother trying to make them last slightly longer. I'd also recommend picking up a bag of size 16 bands here (
http://www.dykemarubberband.com/stationery_rubber_bands.php). The majority of effects I do use size 19 bands, however, a few use one size of each (in particular, i find the size 16s better for broken and restored bands since they're just faster to break, and I also use one band of each size and color for linking effects to better see the difference in the two).
EDIT: I just realized something. On the page linked above to dykema, before you click buy now, it says the contents are 1,450. It's around 1,750 - that's just a mistake.