If you take the thirds to a shop with the gears and lockers you can expect to pay probably 150$-300$ per third to have them installed. If I were you I would just install them your selve. Its not as hard as everyone makes it out to be aslong as you have an axle around so you can crush the crush sleeves. You just need some breaker bars and alot of strenght. Unless you have another way or putting 300-400 ft lbs of tourque on something.
