For anyone who is wondering (why so much for installing gears). Here's my take: I'm an industrial mechanic, and i have rebuilt plenty of gearboxes for various applications, none for automotive but this should still apply. It aint a simple thing to just throw new gears into anything. Tolerances have to be real close. Too tight of a gear mesh means instant wear. The oil will not get between the teeth as needed. Too loose and the backlash will wear your gears out just as fast. So just take into consideration the ability of yourself or your mechanic to get the optimal space that is needed between the gears, which is normally in the thousands of an inch range. Good mechanics should be paid well for this IMHO..
