i buy beef tendon from a pet store. they're about $1.50 or $1.75 each. the brand named ones like flossies by merrick (beef tendon in a curly shape) are a lot more expensive. you can get cheaper ones here:
http://www.sitstay.com/store/edibles...2.shtml#ED1010 it's about $4.50 for 6-9 sticks at 3-5 inch long.