Comparable *SOLD* listings on eBay are averaging $500 - $600 unloaded, meaning CPUs, power, RAM, and controller included but no HDD
You may want to consider Supermicro servers too. Great enterprise platform. A 6028U X10DRU comparable to the R730XD with 2x E5-2690v3, 64GB RAM, 12 LFF Bays, 4x 10G-BaseT Ethernet is going for about half of what the Dell is selling for