According to Bruce Bjorkman of MAK, his cookers use about 1/2 pound of pellets per hour when set on "Smoke" (about 175°F). At 450°F, the high temp, they burn about 2.3 pounds per hour. This is about the same average as I have experienced on a variety of pellet eaters. The burn rate will vary somewhat depending on the outside air temp, and how much cold meat is loaded in the grill, but cooking load should not have a major impact. Cooking pellets run about $1 per pound depending on the wood flavor, brand, if you get them on sale, and if you have to pay shipping. As a point of comparison, Kingsford briquets list for about $0.75 per pound, but they don't pack the same BTUs because there are fillers. I usually buy 40 pound bags of BBQr's Delight pellets from BigPoppaSmokers.com for $45 and shipping is free to IL. That's $1.13 per pound. That means that if I cook a slab of spareribs for six hours at 225°F I will probably burn about 4 pounds at about $4.50. If I put 8 slabs in there in rib holders, and allocate 1/2 slab per person, my cost for 16 people is about $0.28 each. If I grill a mess of chicken parts at about 325°F for about 1 hour, I will use about 1.5 pounds of pellets for a cost of $1.70.
Although these are marketed as grills, they do much more, including baking or roasting. Because they heat by convection, you might not get the grill marks that a gas or charcoal grill will give you, but you also won’t have the flame-up problems. While many pellet grills offer high cooking temperatures, the maximum depends on ambient temperature and wind. Many users wrap their grills in special insulating covers to help maintain heat, reduce fuel use, and reach the higher temperatures they desire.