This will be inexpensive, easy, and will not take long to construct.
Things you will need:
(1) Drinking Straw from a fast-food restaurant whose name begins with "Mc" and ends with "Donald's".
(4) 9mm neodymium magnets
(2) Drops of cyanoacrylate - super glue
(1) Standard sheet of general purpose printer paper
(1) InkJet or LaserJet printer - or crayons, markers, watercolor, any pigment you can apply...
(1) Scissors or sharp blade
(1) Surface to attach the finished target
(1) Area open enough to toss the projectile
(Please excuse the b-grade post-production. I had 32 minutes until deadline when I started shooting. All needed steps and considerations are present.)