Lamb is sold on hanging weight, the weight after butchering, but before cutting into into individual pieces. Depending on your instructions to the butcher you'll take home 60% - 70% of the hanging weight.
The cost of pork is $11 per pound, plus processing ($50/ half or $100/ whole)
An average lamb will weigh around 60 lbs.
A whole lamb (including processing) will cost approximately $760, a half around $380
Lamb will yield between 60 and 70% take home weight, depending on your cutting instructions. (So you'll have about 40 lbs of meat in your freezer from a whole lamb.)