You have two sizes to choose from: a mini Sackboy that is about 4 inches in height for about $12 USD or a larger 10 inch one for $23. The mini version will be released in November in Japan and come in the 4 varieties: normal, solider, pirate and smile. The larger version only comes in the normal or pirate versions and will be released in December. Each Sackboy is made of a soft material, so Sackboy doesn't actually feel like a sack when you try to cuddle with him.
Fortunately, we know Sackboy plushes are headed to the US as well. Hopefully we'll hear something soon.