Building or upgrading a homelab, NAS or AI rig? The sticker price is the least useful number on an eBay listing. What matters is how much you pay for each unit you actually get: each terabyte, gigabyte of RAM or VRAM, CPU core or watt-hour of battery.
Why price per unit matters
A 4 TB drive for $70 looks cheap next to a 20 TB drive for $260. Per terabyte, though, the first one costs $17.50/TB and the second one $13/TB. The same trap exists everywhere:
- Hard drives and SSDs β compare $/TB, then filter by interface (SATA, SAS, NVMe) and capacity.
- RAM β compare $/GB within one generation (DDR4, DDR5, server ECC).
- GPUs for local LLMs β VRAM is usually the bottleneck, so $/GB of VRAM beats the card's price as a metric.
- Server CPUs and servers β $/core shows which used Xeon or EPYC platform gives the most compute for the money.
- 10GbE gear β $/port for NICs and switches.
- LiFePO4 batteries and power stations β $/kWh, handy for a UPS or off-grid setup.
Doing it without a spreadsheet
I got tired of doing this math by hand, so I built PerUnitPrice. It pulls new and used listings from eBay several times a day, normalises them and ranks them by price per unit. You can filter by capacity, interface, brand, socket or voltage and go straight to the listing.
Tips before you buy used gear
- Check the seller's rating and return policy, especially for enterprise hardware.
- For used drives, ask for SMART data (power-on hours, reallocated sectors).
- For server RAM, match the type (RDIMM vs LRDIMM) and rank to your board.
- Count the hidden costs: shipping, caddies, rails, adapters, cables.
What metric do you use when shopping for homelab hardware? Feedback on the site is very welcome in the comments.
