SPOBI.
First thing: Never buy used gears unless you're confident in the seller and his reasons for selling used gears.
Second: Unless you're gonna install the gears yourself (not recommended unless you truely know what you're doing and have the right tools - I don't even install my own gears......), you're looking at a minimum of $200 per axle for install, $90 - $130 per axle for the master install kit, and then the cost of the gears........ and don't forget that for the most part, gear sets 4:10 and higher will require a different carrier, or a full carrier locker to install them.
But it's true - if you're patient, you can score built axles ready to bolt in every now and then........ Just ask Beezle - $600 for a matched set HP D30/8.25 with 456's, EZ locker in front, Powertrax lunchbox for the rear. (God, I musta been insane....... :doh
BTW: Anyone wanting to have their axles professionally re-geared, get with Terry (87xjco) - he cuts as good a deal as there is out there and has/will do all my gear work. :thumbup: ......... unless Led will do it for free...... :laugh3: