You can go to an Office Depot and buy a big bag of #64 rubber bands pretty cheap.

http://www.officedepot.com/ddSKU.do?...g=true&An=text

or

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXL434

You decide. Don't reuse too often and clean well if you do.

About 10-12 per assembly.

OK, no Office Depot near you but you get the idea.