It all depends on how often the pivot has been serviced. If the gearboxes all have oil in them, and no water, they will last the season without issue. If the tires are checked and at the proper inflation they will probably last fine. If a tire does goes flat, by the time you catch it, the tire is already wrecked, and they are rather expensive (at least up here) to replace. On the order of $350 CAD.
We run 18 pivots and we usually have to replace at least 2-3 tires and usually just a couple of gearboxes each year.
With the cost of water and electricity alone, we figure irrigation costs us about $50/ac. Alberta's line transmission charges are out of control up here, which contributes to the cost.