Those batteries are far too chunky... and you can get 100 of any colour 10mm LEDs for $15 shipped elsewhere. I _could_ pay twice the price and get everytihng from dealextreme, but there are some batteries and magnets that work and some that don't. I've been building throwies for long enough to know which are which.
By the way... you need 10 mil LEDs.
So as it stands. The prices are $0.45 for 400 and if we can make 500, $0.34 each (adding a cent or so each offsets postage costs). Hell if we make 400 I'll pay for another hundred myself.