77 ft-lbs is correct.It's fairly low torque - 77 ft/lbs I believe. That's why impact guns at around 150 ft/lbs are a bit much on our cars.
Most (not all) places use a torque stick, with most (again not all) being at 80 ft-lbs, on the end of their impact wrench when putting wheels back on as most (again not all) cars are around 80 ft-lbs (yes, many are different both higher and lower -- 94 ft-lbs for my wife's minivan for example). No car that I am aware of has 150 ft-lbs torque spec for the wheel bolts, therefore if a mechanic is using a bare impact wrench w/ 150 ft-lbs torque they really have no clue and you should not use their services at all.
To the OP, $75 is about what it costs here to have 4 tires mounted. Stick on weights usually cost more than the clamp on weights which can also account for some of the price.