Throwies are awesome, they inspire folks to do more, about a year ago I tried my first flying Throwies, and had a few problems(indoors helium balloons filled to the max pop very loudly). I will quickly in this short Instructable show how to do it, as cheaply as possible, and avoid the problems I ran into.
Step 1: Ingredients.
1 helium grade party balloon, 18 inch or so
1 LED (I used a blinking red)
1 CR1025 3volt lithium battery, you could use a cr2012 or cr2032 but they are big and heavy and the balloon needs to be inflated to near bursting.
Some electrical tape(I love the 3m clear electrical tape, but I could not find my roll (perhaps its too clear! ;-))