LED throwies consist of only a few inexpensive parts and can be made for ~$1.00 per Throwie. You can reference the parts list below or download the attached spreadsheet for more info on parts, part's numbers, vendors and application notes.
Part: 10mm Diffused LED
Vendor: HB Electronic Components
Average cost: $0.20 avg per LED
Notes: Cost reductions for larger quantities. Comes in red, blue, amber, white in both diffused and clear. Diffused works better than water clear for the Throwie application. HB has even created a Throwies packs
page with deals on 10mm LEDs and lithium batteries!
Part: CR2032 3V Lithium Batteries
Cost: $0.25 per battery
Notes: Cost reductions for larger quantities. With the 2032 Lithium batter, depending on the weather and the LED color, your Throwie should last around 1 -2 weeks.
Part: 1-inch wide Strapping Tape
Vendor: Your local hardware store
Cost: $2.00 for one roll
Notes: One roll will make many throwies
Part: 1/2" Dia x 1/8" Thick NdFeB Disc Magnet, Ni-Cu-Ni plated
Cost: $13.00 per 25 magnets
Notes: Cost reductions for larger quantities
Part: Conductive Epoxy
Vendor: Newark In One
Notes: The epoxy is optional.