Honestly $2500 for a good pair isn't too crazy. For that price I would want to open them both up, do a visual check and check backlash with a dial indicator. You can find cheaper if time is on your side. Once in a blue moon a K30 will hit a pick-n-pull yard, slightly more often a dually will. Trying to find a unicorn is easier than a cheap kingpin Dana 60.
This is how my axle costs broke down.
$800 for a used DRW GM kingpin Dana 60 with 4.10 gears out of a dually pickup.
$300 for new SRW hubs with rotors.
$100 for new bearings.
$200 for rear SRW 14 bolt FF with 4.10 gears and evil govloc.
$125 for another 14 bolt FF that had an open carrier (you need an open one for a Detroit locker)
$550 for a new Detroit locker
Grand total... $2,075.00
I could have spent less if I did not buy the axle with the govloc, but even trying to be thrifty I spent about $2000 and drove all over to pick up everything, then a few months later I took out the 4.10 gears and put in 4.88 gears.
The rear axle picture you posted is of a semi floater. A full floater will have a spindle and a hub. The drive flange of the axle bolts to the hub, and the axle supports no weight. A semi floating axle will have a single outboard bearing and the axle supports the vehicle weight. A dually rear axle is full floater.
I think the GMC 3/4 ton pickups and suburban had full floater 14 bolts (K2500), and the Chevy 3/4 ton K20 pickups and suburban had the semi floater 14 bolt rear ends.
