Usually $34.95 US, this weekend you can buy this 5 episode pack and download directly from Telltale for $4.95 US. I believe this works on PC and Mac but you should double check if you are buying for Mac. Vendor deal description follows.
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"Avast me hearties! This Sunday, September 19 be International Talk Like a Pirate Day, and — barnacles be danged — we be celebratin' the entire weekend. The big news: we be takin' our sabers to our beauty of a pirate game and slashin' the price by 30 doubloons so that ye can Play Like a Pirate. This weekend and this weekend only, Tales of Monkey Island be $4.95. Yes, fer the full season, and yes ye be eligible fer the free end-of-season DVD (you pay shipping and handling).
The sale starts now and ends erlie on the morn of Monday September 20 (all times PST). Smartly navigate ye vessel (or ye browser) to our special International Talk Like a Pirate Day page to place yer order before the blasted privateers (or worse, LeChuck) catch wind of the booty and send it to the briny depths of Davy Jones' Locker!"
After buying it, you can then get the Tales of Monkey Island Collector's DVD (which includes the whole season and bonus features) for free (pay $7.87USD shipping). Might not be worth it to some (who'll probably just burn themselves a spare copy), but great if you want their official DVD to store away with bonus features!