He might be exaggerating a bit (who counts at that point anyway?), but it's do-able if you really try. I don't know exactly how fat his blunts are, but if there's at least 1 gram in each blunt (probably more), he's smoking at a minimum close to 3 ounces a day. An ounce of the **** he smokes on probably goes for around 300 a zip; meaning he probably spends about 1,000$ a day in cannabis (assuming he doesn't grow it himself, which is substantially cheaper).
Bob Marley was rumored to smoke a pound a week. Some of his son's admit to smoking an ounce or two a day themselves as well. The most I've ever smoked in a day was last 4/20 when I smoked a half-ounce (**** ain't free).