Costume purchase prices can vary from $30-$200 depending on the quality.
Most people last year bought from santasuits.com for approx $49. There are a TON of places to buy Santa costumes on the web, here are just a few:

CostumesForSanta.com Partycity.com MySantaSuit.com SantaSuits.com SantaPlanet.com SantaClausSuit.com BuyCostumes.com

 

Important:
You Must wear a Santa Suit or a Christmas Themed Outfit to participate.
A pair of Jeans and a Santa Hat does not count!