Here are our Despicable Me costumes from Halloween 2011! These are my sons ages 10, 8, and 5. The minions were completely homemade. They were Halloween witch cauldrons hot glued to a camping mat, then painted yellow. The eyes, goggle straps, hair and mouths were glued on craft foam. I bought fabric and wrapped it around foam for the overalls (I can't sew!!).
The goggles were jewelry cases from a craft store painted silver. I painted on the Gru symbols with fabric paint. I don't believe the minions cost anymore than $50 a piece. The Gru mask we had to buy, but we pieced together things we had to make the suit and added a Gru symbol zipper made with cardboard & fabric paint. The scarf was 2 dollar store scarfs glued together for that perfect "Gru" length.
People went nuts over these. They went Trick-or-Treating at a local mall and a line formed of little kids who wanted to get their pictures with them!