Update: People are able to get all 6 seasons for $29. Click here for more info. Your mileage may vary. Thanks BPHusker.
Best Buy has 24: Season 1 Special Edition on DVD and your choice of any other 24 : Seasons (2 - 6) on DVD for $19. Select in-store pickup to save on shipping. Shipping starts at $1.99 per DVD. Thanks BlueCrown.
Price comparison is for Season 1 Special Edition alone, for example, 24: Season 6 DVD set sells for $30 on PriceGrabber