This is my Alan from The Hangover Costume. The wig and the beard is something you can find at any Halloween costume store (10 bucks for the beard hair, 20 for the wig). I bought the real blue blocker sunglasses for 14.95 online, got the baby Bjorn at a used baby clothes store, only 10 bucks, along with the white baby hat and blue nightie for another 10 bucks.
Pants were thrift store, 4 bucks. The shirt was the same in the movie and was the most expensive item; called 'the human tree' on amazon for 29.95. I also blackened my eye when I took off the sunglasses for when he got punched by Tyson, and wrapped my hand with white tape for when he cut himself in the beginning to be blood brothers.
If you wanna go totally in character, which I did, write out the speech he says on the roof and walk up to people and interrupt them by saying the speech, just replace 'Las Vegas' with wherever you're from. Overall the costume killed, won every costume contest I went to for the week.