Forget alpacas. They're way too small and have light bones. They're only good for about 20 lb. They're used for short day hikes with the kids.
I've never dealt with this place but I've seen their ads online. They rent by however long you want to go.
UTAH LLAMA RENTALS They can tell you what you need to know about rentals.
When my llamas are in good shape, they can handle about 80lb. A saddle, empty panniers, etc add up to about 10lb so figure 70lb. 3 can handle a cow elk, 4 for a bull.